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DIS-2020 is the 28th in the series of annual workshops on Deep-Inelastic Scattering (DIS) and Related Subjects. The conference covers a large spectrum of topics in high energy physics. A significant part of the program is devoted to the most recent results from large experiments at BNL, CERN, DESY, FNAL, JLab and KEK. Theoretical advances are included as well.
Recent measurements in hadron-hadron collisions at RHIC and LHC involving heavy quarks will be presented. The results are related to the production of c and b quarks and the study of quarkonium. Also measurements involving the search and study of exotic final states, such as tetraquark and pentaquark candidates, are presented and discussed.
Detailed measurements of the properties of the 125 GeV Higgs boson are fundamental for the understanding of the electroweak symmetry breaking mechanism. The LHC Run-2 dataset has made it possible to probe a wide range of Higgs boson properties in a variety of decay channels. This talk will summarize recent results from both the ATLAS and CMS experiments.
Recent highlights from experiments involving target and/or beam polarization at BNL, CERN, DESY, Fermilab, and Jefferson Lab are presented. These measurements aim at unraveling proton spin in terms of the contributions from its quarks and gluons; how proton spin is correlated with parton motion inside the proton; and how the proton spin influences the spatial distributions of partons, thus providing a novel multi-dimensional and dynamic picture of the proton.
I will discuss recent progress in the theoretical and phenomenological investigation of the spin structure of the nucleon. In particular, I will report on the status of the verification of the spin sum rule for the proton. I will focus on the possibility to access information on the quark orbital angular momentum from different types of parton distributions, such as transverse momentum dependent parton distributions, generalized parton distributions, and Wigner functions and discuss how these distributions can be used to map out the multidimensional partonic structure of the proton in coordinate and momentum space.
An impressive amount of data from the Large Hadron Collider (LHC) is allowing searches for physics beyond the Standard Model with remarkable reach. Uncovering the mysteries potentially hiding in this data requires a precision understanding of Quantum Chromodynamics (QCD) both for signal and background processes. In this talk I review recent theoretical progress in our ability to understand QCD at the requisite level, focusing on fixed order calculations in perturbative QCD.
Ultraperipheral collisions at the LHC and RHIC offer the highest currently available energy for photon-nucleon and photon-nucleus collisions. Thus they are a valuable tool for studying the gluonic structure of hadrons and nuclei at small x. This talk will discuss experimental results in ultraperipheral collisions, most prominently exclusive vector meson production. We will also discuss recent theoretical work towards understanding such exclusive processes at NLO accuracy in QCD perturbation theory. These theoretical advances are also immediately relevant for understanding the physics of DIS at small x.
To date, LHC experiments are remarkably consistent with Standard Model predictions. Theorists, however, remain convinced of the need for new physics beyond the Standard Model. I will discuss the motivations for beyond the Standard Model physics and speculate as to where cracks in the Standard Model framework are most likely to emerge.
With the pp collision dataset collected at 13 TeV, detailed measurements of Higgs boson properties can be performed. This talk presents measurements of Higgs boson properties using Higgs boson decays to two photons, two Z bosons, and two W bosons, including production mode cross sections and simplified template cross sections.
We present recent results on the analysis of Higgs to WW decays and the corresponding constraints on the Higgs couplings. Focus is concentrated on the recent differential analysis of the Higgs boson transverse momentum and associated production of hadronic jets exploiting the full Run 2 statistics. Recent constraints on new physics models derived from high mass searches in the WW channel are also presented.
The measurement of Higgs boson production in association with a ttbar pair is essential to understand the top-quark couplings to the Higgs boson. This talk presents the analyses using Higgs boson decays to bbbar pairs, to two Z bosons, to other multi-lepton final states, and to a pair of photons, using pp collision data collected at 13 TeV.
Precise measurements of the Higgs boson Yukawa couplings are important tests of the Standard Model of particle physics. In this talk, the most recent results of the analyses performed by the CMS experiment studying Higgs boson decays to fermions will be presented.
In this talk LUXE (Laser Und XFEL Experiment) is discussed. It is an experiment that aims to use the high-quality and high-energy electron beam of the European XFEL and a powerful laser. The scientific objective of the experiment is to study quantum electrodynamics processes in the regime of strong fields. High-energy electrons, accelerated by the European XFEL linear accelerator, and high-energy photons, produced via Bremsstrahlung of those beam electrons, colliding with a laser beam shall experience an electric field up to three times larger than the Schwinger critical field (the field at which the vacuum itself is expected to become unstable and spark with spontaneous creation of electron – positron pairs) and access a new regime of quantum physics. The processes to be investigated, which include nonlinear Compton scattering and nonlinear Breit-Wheeler pair production, are relevant to a variety of phenomena in Nature, e.g. in the areas of astrophysics and collider physics and complement recent results in atomic physics. The regime of multi-photon exchange is also of interest for QCD; it is similar to the color-glass condensate there.
The experimental setup requires in particular the extraction of a minute fraction of the electron bunches from the European XFEL accelerator, the installation of a powerful laser with sophisticated diagnostics, and an array of precision detectors optimised to measure electrons, positrons and photons. Physics sensitivity projections based on simulations are also shown.
The LHeC and the FCC-eh are the cleanest, high resolution microscopes that the world can build in the nearer future. Through a combination of neutral and charged currents and heavy quark tagging, they will unfold the parton structure of the proton with full flavour decomposition and unprecedented precision. In this talk we will present the most recent studies on the determination of proton parton densities as contained in 2020 White Paper on the LHeC.
SoLID spectrometer was proposed to fully exploit the potential of JLab 12 GeV energy upgrade. It is a large acceptance detector which can handle very high luminosity. An overview of the exciting rich physics program will be given, which includes a number of planned measurements: a multi-dimensional mapping of semi-inclusive DIS asymmetries to reach ultimate precision for tomography of the nucleon in momentum space in the high-x region; a measurement of parity-violating DIS to provide a precision test of the Standard Model, reaching a sensitivity to new physics at 10-20 TeV level; a precision measurement of J/ψ photo- and electro-production cross sections in the threshold region to probe the strong color fields in the nucleon and to study the origin of the proton mass. The status and the plan of the project will be discussed.
The LHCb detector is currently being upgraded to be able to take data at higher luminosities and with greater efficiency in Run3. This involves replacement of many subdetector systems, including the vertex detector, upstream tracker, the photodetectors of the ring-imaging Cherenkov detectors, and the downstream tracker. Equally important will be a complete redesign of the data-acquisition system, eliminating the hardware trigger. Physics goals with Run-III data and the status of ongoing and planned detector upgrades will be presented. A brief view on software upgrades and an outlook towards HL-LHC will also be shown.
The Pierre Auger Observatory is the world's largest detector for the observation of ultra high energy cosmic rays (UHECRs). We use a series of fluorescence telescopes and a particle array at the surface to obtain detailed measurements of the energy spectrum, mass composition and arrival directions of primary cosmic rays with energies above 10^17 eV with accuracy not attainable until now.
The data collected at the Observatory over the recent 15 years show the suppression of the cosmic ray flux at energies above 5x10^19 eV. In addition, the UHECR mass measurements indicate a mixed composition, rather than a pure light or heavy one. This result suggests that the spectrum suppression may be related to a limit of cosmic ray acceleration at sources, rather than to a propagation effect. However, the composition measurement is heavily influenced by uncertainties in hadronic interaction properties at ultra-high energies. A precise measurement of the muon component of air showers is the key to disentangle the cosmic ray composition from the influence of interaction properties, which leads to a better understanding of the origin of the spectrum suppression. This is also a main motivation for the ongoing upgrade of the Observatory.
In addition, the Auger surface detector array is sensitive to showers induced by ultra high energy neutrinos of all flavours and photons. Recent neutrino and photon limits provided by the Observatory constrain models of the cosmogenic neutrino production as well as exotic scenarios of the origin of UHECRs, such as the decays of super heavy particles.
In this paper the recent results on measurements of the energy spectrum, mass composition and arrival directions of cosmic rays, and future prospects are presented.
The LHCb collaboration has measured cross sections for production of two charmed-particles in pp collisions. These include opposite-sign and same-sign open-charm pair production where the former is dominantly produced in a single parton scattering (SPS) but the latter can be used to study double parton scattering (DPS). In this work we have set up a NLO pQCD framework to calculate double D-meson production based on PDFs and D-meson fragmentation functions taking into account both the SPS and DPS contributions. The latter contribution is estimated with an effective cross section approach where the partonic correlations are neglected. We find a good agreement with the LHCb data when using values for the effective cross section consistent with other measurements. We compare the obtained results also to Pythia Monte Carlo simulations. Furthermore, we calculate predictions for double D-meson production in pPb collisions where the role of DPS is further enchanced due to several proton-nucleon scatterings and predict that the cross sections should be large enough to be measured at the LHC with reasonable statistics. We also discuss the role of enhanced DPS contribution in the two-particle azimuthal correlations whose disappearance in the away-side is predicted to be a signature of saturation phenomena.
Measurements of W/Z-boson production in association with jets provide important tests of perturbative QCD prediction and also yield information about the parton distribution functions of the proton. First, differential cross-sections for Z-boson production in association with jets using proton-proton collisions collected by the ATLAS experiment at √s = 8 TeV are presented. The data are compared to next-to-leading order QCD calculations and predictions from a variety of different parton distribution functions. In addition, if available, differential cross sections are presented for Z-boson production in association with heavy-flavour jets at √s = 13 TeV. The data are compared to theoretical predictions provided by various Monte Carlo event generators. Finally, if available, an analysis on final states with large missing transverse momentum in association with at least one energetic jet, dominated by processes like Z boson decaying into two neutrinos and W boson decaying leptonically associated with jets, at √s = 13 TeV will be presented.
Measurements of electroweak bosons produced in Pb+Pb collisions as well as photon and jet production in small collision systems are of great interest to understanding the partonic structure of heavy nuclei, and serve as a constraint on the initial state in large collision systems. These channels are sensitive to a broad set of physics effects such as the modification of the parton densities in nuclei, including the onset of non-linear QCD or saturation effects at low-$x$, and the energy loss of partons in the nucleus before the hard scattering. This talk presents results on photon and dijet production in $p$+Pb collision data recorded in 2016 by the ATLAS experiment. Measurements of forward-forward and forward-central di-jet yields and azimuthal angular correlations are reported in 5.02 TeV $p$+Pb and $pp$ collisions, including jets up to $y = 4$ in the center of mass frame. Photon yields are reported in 8.16 TeV $p$+Pb data over a wide kinematic range, $p_T$ = 25-500 GeV and $|\eta| <$ 2.37, and the production rates are compared to an extrapolated $pp$ reference based on existing 8 TeV collision data. The measured spectra are used to construct nuclear modification factors and forward/backward ratios. These are compared to theoretical calculations of initial state energy loss and to the expectations from the modifications of parton distribution functions in nuclei. This talk also presents ATLAS final results on W and Z boson production in 5.02 lead-lead collisions and photon and dijet production in $p$+Pb collisions. The resulting W and Z nuclear modification factors are shown differentially in pT, rapidity and centrality.
Observables sensitive to saturation in DIS will be reviewed. Particular triggers on final state particles in DIS make unitarity limits and saturation prominent. Perhaps surprisingly, it appears that one can even trigger on events where unitarity limits are visible for quark-antiquark dipoles, due to gluon saturation, but where quark occupancies are below saturation.
I will present the most recent developments on the reformulation of small x physics in terms of TMD distributions, and how it allows to study spin physics without going beyond the eikonal approximation.
Color charge correlations in the proton at moderately small $x \sim 0.1$
are extracted from its light-cone wave function. The charge
fluctuations are far from Gaussian. Correlators are described by
n-body GPDs which exhibit interesting dependence on impact parameter
as well as on the relative transverse momentum (or distance) of the
gluon probes.
Furthermore, this analysis provides initial conditions for small-$x$
Balitsky-Kovchegov evolution of the dipole scattering amplitude which
include impact parameter and $\hat{r}\cdot\hat{b}$ dependence, and with non-zero $C$-odd
component due to three-gluon exchange.
The color charge correlators could be measured through various
exclusive processes at a high-luminosity EIC.
Calculations at small $x$ are usually made in the eikonal approximation. This is the case in the Color Glass Condensate (CGC) effective theory where the propagation of high energy partons in the intense colour field of a hadron or nucleus, approximated by a shockwave, is described by Wilson lines. In this talk we will review attempts to go beyond the eikonal approximation in the CGC framework, by considering corrections due to the finite length of the target as done in jet quenching studies. We will show the implications in the case of collisions between dilute objects (proton-proton) for single and double inclusive particle production. We will analyse how the non-eikonal corrections give rise to azimuthal asymmetries that vanish with increasing rapidity separation and collision energy. We will finally comment on ongoing attempts to extend these calculations to the dilute-dense situation, thus for proton-nucleus collisions.
We report on the first simultaneous extraction of unpolarized parton distributions and fragmentation functions from a global QCD Monte Carlo analysis of inclusive and semi-inclusive deep-inelastic scattering, Drell-Yan lepton-pair production, and single-inclusive e+e- annihilation data. We use data resampling techniques to thoroughly explore the Bayesian posterior distribution of the extracted functions, and use k-means clustering on the parameter samples to identify configurations that give the best description across all reactions. Our analysis reveals significant correlations between the strange quark density and the strange-to-kaon fragmentation function needed to simultaneously describe semi-inclusive K production data and inclusive K spectra in e+e- annihilation, and suggests a suppression of the strange quark distribution at intermediate x values.
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We present a new approach to performing Bayesian inference for QCD analysis of nucleon structure and hadronization, using machine learning to construct the inverse function mapping quantum correlation functions to observables. The new concept provides an alternative paradigm to the standard maximum likelihood or Bayesian posterior sampling methods. The effectiveness of the new technology is illustrated with application to the extraction of parton distribution functions from deep-inelastic scattering data, with results compared to recent global QCD analyses.
We present a constrained analysis of the valence transversity Parton Distribution Functions from dihadron production in semi-inclusive DIS. While usual extractions of the transversity distributions rely explicitly on the fulfilment of the Soffer bounds, our analysis releases that implicit restriction to implement further explicit constraints through the Lagrange multipliers method. The results are quantitatively comparable to previous analyses in the kinematical range of data ; the qualitative impact of the chosen fitting strategy translates into an increased flexibility in the functional form. We will discuss the resulting tensor charge as compared to other phenomenological and lattice determinations.
Recently, a new global Monte Carlo analysis of parton distribution functions (PDFs) of the pion determined its valence quark distribution using Drell-Yan data from Fermilab and CERN and its sea quark and gluon PDFs from leading neutron electroproduction data from HERA [1]. While that analysis provided greater constraints at small parton momentum fractions $x$, the pion's gluon PDF remains poorly known at large values of $x$. In the present study, we explore the extent to which transverse momentum ($p_T$)-dependent Drell-Yan cross-section data can provide for greater sensitivity to the pion’s gluon PDF at large $x$. We present the results of a combined QCD analysis of all available $p_T$-integrated and $p_T$-dependent pion data. This will provide the most complete imaging of the PDFs in the pion to date across all momentum fractions as well as serve as the first successful simultaneous fit of $p_T$-integrated and $p_T$-dependent pion data at low energies.
We report an update of the ABM PDF fit with a focus on the impact of recent data from the LHC, in particular the ones on W- and Z-boson and not-resonant lepton pair production. Different
approaches to generation of the nucleon photon distribution are considered within the ABM framework and compared to the relevant data. The updated values of strong coupling constant and the heavy quark masses, which are determined from the fit simultaneously with the PDFs are presented.
The final CT18 global analysis released at the end of 2019 is based on the most complete combination of LHC and non-LHC experimental measurements to date. We discuss implications of this expansive data set for the understanding of the unpolarized PDFs and introduce several alternative fits to explore a number of critical features: the PDF pulls of the high-precision ATLAS 7 TeV W/Z data (CT18A); the effects of altering the QCD scale choices for the low-x HERA DIS data (CT18X); and the sum of these changes, including variations of the charm mass (CT18Z). We also examine theoretical predictions based upon CT18 at NNLO and NLO for several standard candle LHC cross sections, parton-parton luminosities, and PDF Mellin moments.
I will give an update on the latest major PDF update with the MSTW/MMHT
framework. The update includes the effects of numerous new data sets, mainly
from the LHC. This includes vector boson production, differential in rapidity,
mass or p_T, or usually some combination. We also include new jet data and
inclusive and differential top pair producation data. There have also been
improvments in the theoretical framework. The parameterisation has been
extended and made more flexible, and more data sets are included without any
approximation at NNLO. The PDFs are largley stable compared to MMHT2014, with
the major changes being in the dteailed breakdown of the quarks and antiquarks
into different flavours. A brief discussion of the dependence on the strong
coupling and quark masses is included.
Apart from a few anomalies, the majority of measurements at the LHC have been consistent with the Standard Model (SM). Searches of new physics signals beyond LHC energies is now being realized by studying available data with an effective field theory framework. In this talk, I present the results from a combined analysis of top quark and Higgs production measurements at the LHC using SM Effective Field Theory (SMEFT) formalism and the SMEFiT fitting methodology. The analysis extends the most comprehensive top quark study to date by adding Higgs production measurements and constraining simultaneously the 60 Wilson coefficients associated with dimension-6 operators in the SMEFT that modify the relevant SM predictions.
The most precise measurements of Higgs boson cross sections, using the framework of simplified template cross sections, are obtained from a combination of the measurements performed in the different Higgs boson decay channels. This talk presents the combined measurements, as well as their interpretation.
The Higgs boson pair production via gluon fusion at high-energy hadron colliders, such as the LHC, is vital in deciphering the Higgs potential and in pinning down the electroweak symmetry breaking mechanism. In this talk, I will present the NNNLO QCD calculations in the infinite top-quark mass limit and predictions for both the inclusive and differential cross-sections. At the inclusive level, the scale uncertainties are reduced by a factor of four compared with NNLO results. Given that the inclusion of the top-quark mass effects is essential for the phenomenological applications, we use several schemes to incorporate the NNNLO results in the infinite top-quark mass limit and the NLO results with full top-quark mass dependence and present theoretical predictions for the cross-sections. Our results provide one of the most precise theoretical inputs for the analyses of the Higgs boson pair events.
The most precise measurements of Higgs boson single and double Higgs production cross sections are obtained from a combination of measurements performed in different Higgs boson production and decay channels. While double Higgs production can be used to directly constrain the Higgs boson self-coupling, the latter can be also constrained by exploiting higher-order electroweak corrections to single Higgs boson production. A combined measurement of both results yields the overall highest precision, and reduces model dependence by allowing for the simultaneous determination of the single Higgs boson couplings. Results for this combined measurement are presented based on pp collision data collected at a center-of-mass energy of 13 TeV with the ATLAS detector.
Top quark production can probe physics beyond the SM in different ways. The Effective Field Theory (EFT) framework allows searching for BSM effects in a model independent way. CMS experiment is pioneering EFT measurements that move towards using full potential of the data in the most global way possible. Searches for flavour-changing neutral currents (FCNC) and anomalous top quark interactions are also being pursued in CMS which are complementary to the EFT approach. This talk reviews the current limits on FCNC searches in the top sector, and EFT interpretations.
The Large Hadron Collider (LHC) has been successfully delivering proton-proton collision data at the unprecedented center of mass energy of 13 TeV. For the next period of data taking (Run 3), the LHC is expected to deliver an additional 300/fb with pile-up conditions similar or exceeding those of Run 2. A high-luminosity upgrade of the LHC - the High-Luminosity LHC (HL-LHC) - is planned after Run 3 to increase the instantaneous luminosity by a factor 5 to 7 compared to the nominal LHC conditions. The HL-LHC aims to deliver to the ATLAS detector an integrated luminosity between 3000 and 4000/fb at a center-of-mass energy of 14 TeV. To cope with the expected data-taking conditions ATLAS is planning major upgrades of all its detector systems. This contribution will review the status of the ongoing Phase-I upgrade construction, under completion for operations in Run 3, and the progress towards the HL-LHC upgrades. An overview of the physics objectives in Run 3 and at the HL-LHC, and of the expected performance of the upgraded ATLAS detector, will be also presented.
The LHeC provides a comprehensive physics programme with strong implications on that of the HL-LHC. We will present a chapter of the 2020 LHeC White Paper, that is firstly the implications of the precise determination of proton PDFs at the LHeC on the measurement of key SM parameters at the HL-LHC: EW mixing angle, W mass and their impact on EW precision measurements. Then we will address the impact of the LHeC PDFs on Higgs measurements at the HL-LHC, and the results for Higgs couplings from a joint ep+pp analysis. We then discuss the impact of LHeC results on high-mass searches. Finally we discuss the impact of ep and eA measurement on the heavy-ion programme at the HL-LHC.
We present a quantitative assessment of the impact the future Electron-Ion Collider would have in the determination of parton distribution functions in the proton and parton-to-hadron fragmentation functions through semi-inclusive deep-inelastic electron-proton scattering data.
Specifically, we estimate the kinematic regions for which the forthcoming data are expected to have the most significant impact in the precision of these distributions, computing the respective correlation and sensitivity coefficients. Using a reweighting technique for the sets of simulated data with their realistic uncertainties for two different center-of-mass energies, we analyse the resulting new sets of parton distribution functions and fragmentation functions, which have significantly reduced uncertainties.
The LHeC and the FCC-eh will extend the kinematic region presently available in DIS to very small values of $x$ in the perturbative $Q^2$ region. Therefore, they will be able to establish the dynamics of the strong interaction at small $x$ or high energies, and unravel the existence of a new non-linear regime of QCD where parton densities are expected to saturate. In this talk we will review the most recent studies as presented in the 2020 LHeC White Paper. On the experimental side, we will show a new study for the determination of the longitudinal structure function. On the phenomenological side, we will analyse the prospects for establishing the existence of saturation through tension in DGLAP fits to the very precise, large acceptance DIS data.
We asses the impact of the future Electron-Ion Collider
on the collinear gluon helicity distribution ($\Delta g$).
In particular, we study the constraining power of longitudinally
polarized inclusive deep-inelastic scattering on $\Delta g$
using the $Q^2$ range covered by the EIC kinematics.
The CLAS12 detector at Jefferson Lab just started to collect data. Making use of the CEBAF high energy (up to 11 GeV) and highly longitudinal polartized (up to 90%) electron beam will cover unexplored territories in electron-scattering physics. Exclusive reactions on nuclons and nuclei will be measured with high precision in high luminosity (up to 10e35 cm-2s-1) experiments. Mapping out a new class of structure functions, GPDs and TMDs, detecting and reconstructing exotic meson and baryon states and accessing nucleons correlations in nuclei, in the next decade, the CLAS12 rich physics program will provide insight in the complex dynamics of the QCD.
In this talk, the CLAS12 detector and JLab Hall-B physics program will be described reporting some preliminary results for flag-ship reactions and plans for future upgrades of the detector.
I present new theoretical results at approximate N$^3$LO for double-differential distributions in top-quark transverse momentum and rapidity. The higher-order corrections are from NNLL resummation of soft-gluon contributions. The corrections are very significant and they reduce theoretical uncertainties. The theoretical predictions are in very good agreement with recent LHC data.
Comprehensive measurements of differential cross-sections of top-quark-antiquark pair-production are presented. The measurements are performed in the lepton+jets and the all-hadronic channels which allow for reconstruction of the top-quark and top-quark-pair kinematic distributions. The two channels are complementary in terms of range and resolution for several variables. Both measurements use data recorded in the years 2015 and 2016 during Run 2 of the LHC. The measurements are compared quantitatively to several setups of next-to-leading order matrix-element generators combined with parton-shower generators. In addition, a total cross-section measurement based on the full Run 2 dataset is presented.
The hard scattering process in which two top-quark-antiquark pairs are produced is also called four-top-quarks production and is predicted to have a small cross-section of 12 fb in the Standard Model. This very rare process has not been observed yet. The background mainly comes from top-quark-antiquark production in association with heavy flavor jets. In this presentation, two analyses are presented aiming at establishing experimental evidence for this process based on the full Run 2 dataset recorded with the ATLAS detector. The first analysis selects events with exactly one charged lepton and several jets or two charged leptons of opposite electric charge. The second analysis is based on a lepton pair with the same electric charge or events with more than two leptons. In both channels multivariate techniques are used to optimize the separation between signal and background events and enhance the sensitivity. Finally, both channels are combined.
We present NLOPS matched predictions for $pp \to \ell \nu_\ell j j b \bar b$ at $\alpha^4 \alpha_s^2$ within the POWHEG BOX RES framework. This process is dominated by top-pair production and decay in the semileptonic channel. The hadronic decay of the W-boson is considered in an approximation that allows for consistent inclusion of the contributions from $t\bar t$ and $Wt$ single-top production and all relevant quantum interferences between different channels.
Latest results on inclusive and differential top quark pair and single top quark production cross sections are presented using proton-proton collision data collected by the CMS experiment. The differential cross sections are measured as a function of various kinematic observables of the top quarks and the jets and leptons of the event final state. The results are confronted with precise theory calculations and used to constrain Standard Model parameters.
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Measurements of top quark properties using data collected by the CMS experiment at 13 TeV are presented. They include direct measurements of properties or extractions using differential cross section measurements. Among them, the latest results on top mass and its running, top Yukawa coupling, the top sector of the CKM matrix, ttbar forward backward asymmetry will be discussed.
Inclusive single diffractive dissociation (pp->pX) is studied using data collected by the ATLAS experiment at the LHC. The intact proton is reconstructed and measured in the ALFA forward spectrometer, while charged particles from the dissociative system (X) are reconstructed and measured using the ATLAS inner tracking detector and calorimeters. Differential cross sections are presented as a function of the proton fractional momentum loss, the four-momentum transfer squared, and the size of a rapidity gap measured from the edge of the ATLAS calorimeters. The results are interpreted in the framework of Regge phenomenology. If available, an additional measurement of the properties of the dissociative system is presented for events with a proton reconstructed in the AFP detector. Finally, if available, a measurement of elastic scattering is presented at √s =8 TeV, using forward protons reconstructed in the ALFA spectrometer.
We present the first measurements of diffraction in $\sqrt{s_{NN}}=8.16$ TeV proton-lead collisions within CMS. The very large angular coverage of CMS is used to tag rapidity gaps on both the proton-going and lead-going sides and to identify both pomeron-lead and pomeron-proton topologies. Since the previous highest energy measurement of these processes was at $\sqrt{s_{NN}}=30$ GeV, the current data provides essentially unique information. The rapidity gap distributions are sensitive to the gluon distribution within nuclei but also provide important information for modeling cosmic ray collisions. The results are compared to predictions from the EPOS, QGSJET and HIJING event generators and discussed in the context of other measurements from both pPb and pp collisions. In addition, we present a first measurement of two-particle angular correlations for charged hadrons emitted from photon-proton, $\gamma p$, interactions over a wide range of pseudorapidity and full azimuth. The $\gamma p$ events were produced within ultra-peripheral pPb collisions at $\sqrt{s_{NN}}$ = 8.16 TeV and were selected by requiring a large rapidity gap in the lead-going direction and no neutron emission from the lead nucleus. The results are compared to a sample of minimum-bias pPb events with same multiplicity. The observed azimuthal correlations at large relative pseudorapidity are used to extract the first, second and third-order two-particle anisotropy harmonics, V1D, V2D, and V3D as a function of track multiplicity and transverse momentum pT. For both the photon-p and minimum-bias pPb samples V1D is negative, V2D is positive and V3D is negative but consistent with zero. The single particle second-order harmonic, v2 (pT) is larger for photon-p events than for minimum-bias pPb collisions of the same multiplicity.
The CMS Precision Proton Spectrometer consists of tracking and timing detectors placed close to the beam at about 200m from the interaction point. The goal of PPS is to measure the kinematic parameters of the protons scattered in interactions where at least one of them emerges intact. Silicon tracking detectors measure the momentum lost by the proton and diamond timing detectors measure its time of flight to reduce pileup contributions. The data collected during LHC Run2 correspond to around 100 /fb and are currently used in several analyses that study central exclusive production (CEP), including photon-photon production of W and Z boson pairs, high-mass photon and lepton pairs, high-pT jet production, as well as searches for anomalous couplings and new resonances. Meanwhile, new detectors are being built for LHC Run3.
In the Ingelman-Schlein approach for hard diffraction the cross sections can be factorized into diffractive PDFs and perturbatively calculable partonic coefficient functions. The diffractive PDFs can be determined in a global QCD analysis using data for diffractive processes in DIS in a similar manner as for inclusive PDFs. However, it has been observed that this factorization breaks down in proton-proton collisions as the predicted cross sections overshoot the data by an order of magnitude. Similarly, factorization-based calculations for diffractive dijets in photoproduction at HERA tend to lie a factor of two above the H1 and ZEUS measurements.
Such a breaking of factorization can be naturally explained with multiparton interactions (MPIs) where the additional partonic interactions produce particles that fill the rapidity gap used to select the diffractive events. Following this idea, we have introduced a dynamical rapidity gap survival model for hard diffraction in Pythia 8 Monte Carlo event generator. The model relies on the existing MPI model in Pythia 8 and the generated cross sections are in a good agremeent with the most recent CMS data for diffractive dijet production in proton-proton collisions at the LHC. Here we focus on the recent extension of the model for photoproduction and show that the generated cross sections are well in line also with the measurements at low photon-virtuality in the electron-proton collisions at HERA. Furthermore, predictions for diffractive dijet production in ultra-peripheral collisions at the LHC are provided for different beam configurations and an outlook for photo-nuclear processes is given.
Diffractive Deep Inelastic Scattering – defined by a colorless exchange between the target nucleus and the incoming electron – is sensitive to the geometric structure of hadrons, and hence can be used as a probe for exploring the mystery of confinement and saturation. Experimentally, this process manifests itself by a rapidity gap in the detector between the outgoing nucleus/remnants and the diffractively produced system. In this talk, we will discuss three complementary event kinematic reconstruction methods for exclusive diffractive events: the Scattered Electron method, the Jacques Blondel method, and the Double Angle method; and we will assess their impact on the physics studied in different kinematic regimes. The simulation studies are performed using an e-A event generator made exclusively for diffractive events – Sartre. The output of the Sartre generator is passed to both a fast simulation package (eic-smear) as well as a full Geant4 EIC detector simulation in order to perform the kinematics reconstruction studies. In addition, for diffractive vector meson production, there is a known dependence of the angular distribution of the vector meson decay products on the polarization of the virtual photon. We will describe how we incorporated this effect into the Sartre event generator.
We present our recent analysis on the nucleon and pion gluon distribution functions in the framework of holographic QCD, focusing on the small Bjorken $x$ region. Based on an approximate relation, the gluon distributions are extracted from structure functions of the unpolarized deep inelastic scattering which can be calculated with a holographic QCD model, assuming the Pomeron exchange in the five-dimensional AdS space. All the adjustable parameters included in the model are determined with the HERA data of the proton structure functions. We show that the extracted proton gluon distribution is consistent with results of the known global QCD analysis. The structure functions of the pion can be computed without any additional parameter, which enables us to predict its gluon distribution also. We find that the resulting pion gluon density is smaller than the proton's, and agrees with the recent global QCD analysis result within the uncertainties.
We present a new global QCD analysis of inclusive unpolarized and polarized DIS data, using a Monte Carlo approach to simultaneously extract both the spin-averaged and spin-dependent PDFs. We focus on the high-$x$, low-$W$ region, where effects from power corrections, such as target mass corrections (TMCs) and higher twists, are particularly important. We quantify the effects on the extracted PDFs from various theoretical treatments of the power corrections and cuts on the experimental kinematics.
Jet production is the primary signal for hard scattering of the partons inside protons, which is one of the dominant processes in proton-proton collisions at the RHIC energies. The jet double-spin asymmetries $A_{\text{LL}}$, measured at the STAR detector in polarized $pp$ collisions, remain one of the main sources of constraint for the polarized gluon parton distribution function $\Delta g$. An earlier STAR jet measurement at the center of mass energy $\sqrt{s} = 200$~GeV provided the first-of-its-kind, clear evidence for the non-zero gluon polarization at $x \geq 0.05$. This talk presents the latest result from the STAR jet measurement at $\sqrt{s} = 510$~GeV using a year 2012 data set. The new limit of the kinematic reach down to $x \simeq 0.015$ is achieved by our data at $\sqrt{s} = 510$~GeV from both inclusive jets and di-jets. We will also discuss the future opportunities for jet measurements after realisation of an ongoing STAR forward upgrade.
The Solenoidal Tracker at the Relativistic Heavy Ion Collider (STAR) experiment probes the gluon helicity distribution $\Delta G(x)$ using collisions of longitudinally polarized protons at $\sqrt{s} = $ 200 GeV and $\sqrt{s} =$ 510 GeV. Access to $\Delta G(x)$ is possible through the double spin asymmetries $A_{LL}$ in gluon-dominated hard scattering processes of inclusive jet and di-jet production.
Previously published results on inclusive jet processes at $\sqrt{s}=$ 200 GeV and $|\eta_{\mathrm{jet}}| < 1$ are based on data collected in 2009, which correspond to an integrated luminosity ($L$) of 20 pb$^{-1}$ with an average beam polarization ($P$) of 57%. When included in perturbative QCD analysis of global data, they provide evidence for positive gluon polarization for a momentum fraction $x > 0.05$ at a hard perturbative scale $Q^2 = 10$ GeV$^2$. Additional data were collected in 2015 with an approximately twice larger figure of merit $\left(LP^4\right)$. This contribution will cover the status of the analysis of 2015 inclusive jet and di-jet data, as well as, the jet measurements based on the most recent high-luminosity 510 GeV data collected in 2013, which will further constrain $\Delta G(x)$ at lower $x$.
Measuring the gluon spin contribution to the proton spin has been one of the main goals of the RHIC spin program. The PHENIX experiment has extracted double longitudinal spin asymmetries which are sensitive to the gluon spin contribution at intermediate x starting at around 0.01 for central rapidity measurements and even lower for forward measurements. The latest results from the data taking period with the highest collision energy of sqrt(s)=510 GeV, at central rapidities will be reported, including charged and neutral pions as well as the status of the jet asymmetry analysis
At RHIC energies high pT direct photons are mainly produced by the quark-gluon Compton scattering process. Being not disturbed by fragmentation processes, they provide access to initial condition of partonic collisions. Direct photon production in pp collisions serves an ideal probe for gluon parton distribution functions (PDF), whereas quark PDFs are well constrained by deeply inelastic lepton-nucleon scattering. Similarly, longitudinally polarized pp collisions provide direct access to gluon helicity distribution within the proton, and therefore contribute to resolving the long standing puzzle of the proton spin decomposition. We will present the status of the direct photon analysis from pp collisions at sqrt(s)=510 GeV by PHENIX for both unpolarized and helicity dependent measurements, and comparison to previous measurements at different sqrt(s) and to NLO pQCD calculations.
The virtual photon asymmetry $A_1$ is one of the fundamental quantities that provide
information on the spin structure of the nucleon. The value of A1 at high $x_{Bj}$
is of particular interest because valence quark dominate in this region, which makes
it a relatively clean region to study the nucleon spin structure. There are several
theoretical calculations that apply to the high x valence quark region, and here we
will focus on the neutron $A_1^n$. The neutron $A_1^n$ is predited to be 0 in the
naive SU(6) quark model, while both relativistic constituent quark model (RCQM) and
perturbative QCD (pQCD) predict $A_1^n$ to be 1 at $x$=1. Predictions for the quark
polarization in the nucleon also exist: $\Delta d/d$ is predicted to approach $+1$
in pQCD while RCQM prediction remains negative at the $x\to 1$ limit. The $A_1^n$
experiment during the 6 GeV JLab era showed that $a_1^n$ indeed turns positive at
$x\sim 0.5$, while $\Delta d/d<0$ at $x=0.61$. Subsequent theoretical studies based
on our 6 GeV results claimed that quark orbital angular momentum or non-perturbative
nature of the strong interaction plays a significant role in the valence quark
region.
With the 12 GeV upgrade of JLab, a new experiment on $A_1^n$ is being carried out
using a 10.4 GeV beam, a polarized $^3$He target, and the HMS and the Super-HMS
(spectrometers) in Hall C. This measurement will reach a deeper valence quark
region: $x\sim 0.75$. And once combined with expected data from the upgraded CLAS12
experiment on the proton $A_1^p$, we will finally be able to reveal whether $\Delta
d/d$ turns positive (as in pQCD) or remain negative at high $x$ (as in RCQM).
We will present the physics of $A_1^n$ and review the running status of the
experiment. Performance of an upgraded polarized $^3$He target will be presented.
The transverse momentum dependent parton distribution functions (TMDPDFs) measure the transverse momentum of partons in a fast moving hadron, and is an important observable for the Electron-Ion Collider. The energy evolution of TMDPDFs is given by the Collins-Soper (CS) anomalous dimension, or the CS kernel, which is essential to the fitting of TMDPDFs from global cross section data at different energies. At small transverse momentum, the CS kernel is nonperturbative and can only be determined from global fitting or first principle calculations. In this talk, I present an exploratory calculation of the CS kernel from lattice QCD using the large-momentum effective theory, which is a systematic approach to extract light-cone parton physics. Our preliminary results show that it is promising to achieve precision calculation with currently available computing resources, which has the potential to be used in the global fitting of TMDPDFs in the future.
We present results on the nucleon valence quark distribution extracted from Lattice QCD simulations, using a gauge ensemble of $N_f=2+1$ Wilson-Clover fermions with a pion mass of $m_\pi = 350$ MeV and lattice spacing of about $a=0.093$ fm. We obtain reduced Ioffe Time Distributions (rITDs) by computing appropriate matrix elements on the lattice, and elaborate on the extraction of the desired quark distributions from the rITDs following the pseudo-PDF approach. In our evaluation, the so-called “distillation” smearing method is employed, which allows for improved statistical precision over other methods, among other benefits. A number of techniques in order to ensure ground state dominance are further considered. Theoretical and experimental implications of our calculation are discussed.
In recent years, parton distributions have been calculated from ab initio QCD using non-perturbative lattice field theory. In this presentation, I focus on a Lorentz invariant generalization of the Ioffe time distribution which can be calculated directly on the Lattice. Just like experimental cross sections, these matrix elements can be factorized into the PDF. I present our latest results for the nucleon and pion unpolarized iso-vector PDF which are testing the systematic errors of these calculations, including an extrapolation to physical pion mass, discretization errors, and finite volume errors.
An understanding of the partonic structure of hadrons is an essential ingredient in making precise predictions and measurements of hadronic cross-sections and various Standard, and Beyond Standard, Model parameters. Direct first-principles calculations of parton distribution functions (PDFs) via lattice QCD (LQCD) were historically limited to the lowest few moments, principally due to the time-dependence of PDFs and the breaking of rotational symmetry via the lattice cutoff. Several encouraging proposals have since been developed that relate lattice calculable quantities with PDFs via frameworks akin to QCD factorization. We report results of one such LQCD formalism, wherein the pion valence quark distribution is extracted through a short-distance collinear factorization of space-like separated vector and axial-vector current correlations. Together with the NLO perturbative kernel for this current combination, computations on four distinct gauge ensembles quantify the systematics inherent in this approach. These data when parametrized with a flexible $z$-expansion fit supplemented with lattice correction terms, yield a physical limit valence distribution that is found to be consistent with experiment across the entire Bjorken-$x$ region and favors a softer approach to $x=1$.
We present our high-statistics lattice QCD determination of the valence PDF of 300 MeV pion using the quasi- and pseudo-PDF (reduced Ioffe-time distribution) formalisms. For the first time in such lattice computations of PDF, we employ two different fine lattice spacings of 0.04 and 0.06 fm, which thereby enables us to use pion boosted to large spatial momenta up to 1.92 GeV that is essential for the perturbative matching framework. Through a model independent analysis of the non-singlet reduced Ioffe time distribution, we extract the second moment $\langle x^2\rangle $ and the fourth moment $\langle x^4 \rangle$ in $\overline{\rm{MS}}$ scheme. Through a model dependent analysis, we extract the pion valence PDF that best describes our lattice data, enabling us to study the behavior of the valence PDF at large-$x$.
We present new lattice QCD calculations for unpolarized and helicity isovector parton distribution functions of nucleons. Lattice QCD calculations were carried out within the framework of large momentum effective theory (LaMET), using a superfine lattice spacing 0.042 fm and boosted nucleons with momenta up to 2.31 GeV. We compare our QCD-based results with those obtained from global fits, and test ranges of applicability of the LaMET approach in realistic lattice QCD calculations.
We present the first attempt to access the x-dependence of the gluon polarized and strange parton distribution functions (PDFs) from lattice calculations, using large-momentum effective theory (LaMET). LaMET methods have been applied to a wide variety of isovector nucleon distributions and valence pion distributions. However, the polarized gluon and strange-quark distributions have not yet been studied. This work carried out the first such lattice calculation with pion masses of 340 and 678 MeV with 3 lattice spacings. We compare the lattice results with the Fourier transform of selected global fits in coordinate space and discuss future prospects.
Lattice QCD and global PDF analyses have both made significant strides in recent years. Much of this progress owes to the growing availability of computational resources as well as steady theoretical advances in lattice gauge theory and perturbative QCD. In this context, it is increasingly suggested that the output of lattice QCD calculations could serve as important input to global fits for PDFs (and related quantities). In this talk, I will discuss this possibility, demonstrating the important role global analyses will play in benchmarking improvements in lattice calculations. I will stress that, going forward, the relationship between lattice QCD and global analyses will provide a powerful basis to improve knowledge of hadron tomography in the EIC era.
Most hard scattering processes at the LHC lead to breakup of the proton because of the single-parton exchange of the proton. However, since the proton is an electrically charged object, quasireal photon-exchange interactions can also take place. Since photons are color-singlet, sometimes the protons remain intact after the interaction, and these can be detected with forward proton detectors close to the beamline. These interactions open the possibility of studying electromagnetic interactions in energies never explored before. In this presentation, the discovery potential of anomalous quartic gauge couplings in photon-induced reactions at the LHC will be discussed. Special attention is given to constraints on quartic four-photon couplings induced by axion-like particles coupled to the electromagnetic field, which can be probed in the scattering of light-by-light at the LHC, and more generally on studies of yyyy, yyyZ, yyWW, and yyZZ anomalous quartic couplings.
Recent multiboson results at CMS are presented.
Measurements of electroweak boson pair production at the LHC constitute a stringent test of the electroweak sector and provide a model-independent means to search for new physics at the TeV scale. In this talk, we present recent results from the ATLAS experiment for WW, ZZ and Z𝛾 production in proton-proton collisions at √s=13 TeV. The measurements in each channel exploit the leptonic decays of the weak vector bosons. Differential cross sections are measured that probe the topology of each final state. The data are corrected for detector inefficiency and resolution and are compared to theoretical predictions at NLO (and NNLO) in perturbative QCD. The measurements are sensitive to anomalous triple gauge couplings and are reinterpreted in terms of an effective field theory to constrain new physics beyond the Standard Model. In addition, we present a measurement of the Z𝛾 process in which the Z-boson decays to a pair of b-quarks, which probes the reconstruction of hadronically decaying Z-bosons using jet grooming techniques.
We present prospects for the direct measurement of ratios of differential cross sections for the production of Z and Higgs bosons in proton-proton collisions, using data taken by CMS during the LHC Run II. The aim of the study is to investigate soft and hard gluon emission in the initial state for Higgs and Z production mechanisms. Hence, we focus on variables known to be sensitive to the production mechanisms of heavy bosons: jet multiplicity, transverse momenta of the boson and leading jet, and momentum balance in the transverse plane. We use Monte-Carlo samples to study the feasibility of the measurement and estimate the expected precision, and find that visible effects of the difference of production mechanisms could be observed in Run II data.
We present NLO QCD predictions for dijet photoproduction on heavy nuclei for three future collider options at CERN, the LHeC, its high-energy (HE) version and the electron-hadron/nucleus version of the FCC, and compare them to our previous predictions for the EIC. We focus on the potential of these colliders to constrain nuclear parton densities, in particular in the small-x region, based on the current uncertainties of the nCTEQ and EPPS analyses. These global fits are also compared to predictions from the leading-twist nuclear shadowing model.
The proposed high luminosity high energy Electron Ion Collider (EIC) will explore the proton/nuclear structure, search for gluon saturation and precisely determine the nuclear parton distribution functions (nPDFs) in a wide x-$Q^{2}$ phase space. Heavy flavor and jet measurements at the future EIC will allow us to better constrain the nPDFs within the poorly constrained high Bjorken-x region, precisely determine the quark/gluon fragmentation processes and directly study the quark/gluon energy loss within the nuclear medium. We propose to develop a new physics program to study the flavor tagged hadrons/jets, heavy flavor hadron-jet correlations and flavor dependent jet fragmentation processes in the nucleon/nucleus going direction (forward region) at the EIC. These proposed measurements will provide a unique path to explore the flavor dependent fragmentation functions and energy loss in heavy nuclei, which can constrain the initial state effects for previous and ongoing heavy ion measurements at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). To realize these measurements, a forward (proton/nuclei going direction) silicon tracking detector is proposed and the detector R$\&$D and detector design are ongoing with the Los Alamos National Laboratory Lab Directed Research and Developments (LDRD) supports. Details of the proposed new physics program, progresses of the detector and physics simulation studies and the status of the detector R$\&$D will be discussed in this presentation.
The LHeC and the FCC-eh, with its large kinematic reach and luminosity, offer the possibility to study hitherto uncovered, novel properties of QCD. In this talk we will review recent studies as presented in the LHeC 2020 White paper. Among other phenomena, we will discuss topics such as intrinsic heavy flavour, the determination of the running coupling at low scales, the radiation zero amplitude due to EW interferences, and several novel aspects in electron-nucleus collisions.
Recently, there has been increasing recognition that jet measurements can be an important component of the physics program at the future Electron-Ion Collider (EIC). Jets are a more effective proxy for partonic kinematics than the single hadron measurements usually performed in Deep Inelastic Scattering experiments, while substructure techniques can be used to examine non-perturbative effects as well as probe the properties of cold nuclear matter. In addition, the relatively clean environment at the EIC will reduce the complications introduced by large underlying event activity found in high energy pp and AA collisions. This contribution will highlight results from two recent papers, the first of which demonstrates the utility of jets as parton surrogates via measurements of the gluon Sivers function with dijets, and a second that explores the feasibility of substructure measurements at the EIC. Future directions will also be discussed.
Using a newly proposed formalism which generalizes the Color Glass Condensate formalism and extends it to large Bjorken $x$, we calculate the dijet double differential cross section and investigate its properties for different kinematics; from small $x$ to large $x$ and from low to high transverse momenta.
We determine the small Bjorken $x$ asymptotics of the quark and gluon orbital angular momentum (OAM) distributions in the proton in the double-logarithmic approximation (DLA), which resums powers of $\alpha_s \ln^2 (1/x)$ with $\alpha_s$ the strong coupling constant. Starting with the operator definitions for the quark and gluon OAM, we simplify them at small $x$, relating them, respectively, to the polarized dipole amplitudes for the quark and gluon helicities defined in our earlier works. Using the small-$x$ evolution equations derived for these polarized dipole amplitudes earlier we arrive at the following small-$x$ asymptotics of the quark and gluon OAM distributions in the large-$N_c$ limit:
$L_{q + \bar{q}} (x, Q^2) = - \Delta \Sigma (x, Q^2) \sim
\left(\frac{1}{x}\right)^{\frac{4}{\sqrt{3}} \, \sqrt{\frac{\alpha_s
\, N_c}{2 \pi}} }$ ,
$L_G (x, Q^2) \sim \Delta G (x, Q^2) \sim
\left(\frac{1}{x}\right)^{\frac{13}{4 \sqrt{3}} \, \sqrt{\frac{\alpha_s
\, N_c}{2 \pi}}}$.
We find the small-$x$ asymptotics of the quark helicity distribution in the large-$N_c$ & $N_f$ limit by numerically solving small-$x$ evolution equations derived in earlier works, where $N_c$ is the number of quark colors and $N_f$ is the number of quark flavors. Previously, those evolution equations were solved only in the large-$N_c$ limit. We find that $\Delta q$ oscillates as a function of $\ln(1/x)$ at small $x$, with the oscillation frequency being dependent on the number of quark flavors, $N_f$. Our result may account for the apparent oscillation in the strange quark helicity distribution $\Delta s$ as a function of Bjorken $x$. For $N_f=0$, these oscillations disappear; this is why they were not seen in the earlier large-$N_c$ studies. Our work presents the most precise theoretical determination of the small-$x$ asymptotics of the quark helicity distribution based on the Wilson line approach to small-$x$ evolution. When combined with the future EIC data, our approach should allow for a precise determination of the amount of the proton spin coming from small-$x$ partons, thus contributing to the resolution of the proton spin puzzle.
The worldline representation of quantum field theory is a powerful framework for the computation of perturbative multi-leg Feynman amplitudes. In particular, in gauge theories, it provides an efficient way, via point particle Grassmann functional integrals, to compute spinor and color traces in these amplitudes. In my talk I will give a short introduction into the worldline formalism and show how it can be applied to the problem of computation of the polarized deeply inelastic structure function $g_1$ in the small x Regge limit of QCD. In particular, in a shockwave approximation valid in this limit, I will show how one can derive a polarized dipole model. I will discuss computation of sub-eikonal corrections which give rise to the quark and gluon operators of the model and introduce a generalization of the standard McLerran-Venugopalan (MV) model which represents the spin structure of hadrons at small-x.
We calculate the single transverse spin asymmetry (STSA) in polarized proton-proton and polarized proton-nucleus collisions ($A_N$) generated by a partonic lensing mechanism. The polarized proton is considered in the quark-diquark model while its interaction with the unpolarized target is calculated using the small-x/saturation approach [1], which includes multiple rescatterings and small-x evolution. The phase required for the asymmetry is caused by a final-state gluon exchange between the quark and diquark, as is standard in the lensing mechanism of Brodsky, Hwang and Schmidt [2]. Our calculation combines the lensing mechanism with small-x physics in the saturation framework. The expression we obtain for the asymmetry $A_N$ of the produced quarks has the following properties: (i) The asymmetry is generated by the dominant elastic scattering contribution and $1/N_c^2$ suppressed inelastic (color quadrupole) contribution (with $N_c$ the number of colors); (ii) The asymmetry does not fall off with the produced quark's momentum $p_T$ until the momentum reaches the saturation scale $Q_s$, and then only falls off as $1/p_T$ for larger momenta; (iii) The asymmetry decreases with increasing atomic number $A$ of the target for $p_T$ below or near $Q_s$, but is independent of $A$ for $p_T$ significantly above $Q_s$. We discuss how these properties may be qualitatively consistent with the data on $A_N$ published by the PHENIX collaboration [3] and with the preliminary data on $A_N$ reported by the STAR collaboration [4].
\newline
[1]. Iancu, E., Venugopalan, R. (2003), The color glass condensate and high energy scattering in QCD, in \emph{Quark Gluon Plasma}, World Scientific.
\newline
[2]. S. J. Brodsky, D. S. Hwang, and I. Schmidt, Phys. Lett. B530, (2002).
\newline
[3]. C. Aidala et al. (PHENIX Collaboration), Phys. Rev. Lett. 123, (2019) 122001.
\newline
[4]. S. Heppelmann (STAR Collaboration), Preview from RHIC Run 15pp and pAu Forward Neutral Pion Produc-tion from Transversely Polarized Protons, in \emph{Proceedings,7th International Workshop on Multiple Partonic Interactions at the LHC}, (2016) p. 228.
Heavy quarkonium production provides valuable grounds to explore fundamental QCD dynamics with multiple scales. Thus far, NRQCD factorization has been successful in describing many features of the data. Despite many theoretical efforts at NLO accuracy, however, there are still unresolved issues, including the lack of a full understanding of quarkonium polarization at high $p_t$. One significant caveat is that the NRQCD factorization framework does not include the full final state evolution relevant to high $p_t$ quarkonium production. In previous studies [1,2], a QCD factorization formula for high $p_t$ quarkonium production was derived up to next-to-leading power (NLP) in the $1/p_t$ expansion, by including single parton (twist-2) and double parton (twist-4) fragmentation functions. In this talk, we present the first numerical analysis of the scale evolution of the coupled twist-2 and twist-4 fragmentation for quarkonium production [3]. In particular, we will discuss how we succeeded in simplifying the complicated evolution equations [1], using novel input distribution functions [4,5]. We will then pursue the importance of the quantum evolution for solving the quarkonium polarization puzzles at high $p_t$.
[1] Z. B. Kang, Y. Q. Ma, J. W. Qiu and G. Sterman, Phys. Rev. D 90, no. 3, 034006 (2014).
[2] Y. Q. Ma, J. W. Qiu, G. Sterman and H. Zhang, Phys. Rev. Lett. 113, no. 14, 142002 (2014).
[3] K. Lee, J. W. Qiu, G. Sterman, and K. Watanabe, in preparation.
[4] Y. Q. Ma, J. W. Qiu and H. Zhang, Phys. Rev. D 89, no. 9, 094029 (2014).
[5] Y. Q. Ma, J. W. Qiu and H. Zhang, Phys. Rev. D 89, no. 9, 094030 (2014).
The Belle II experiment at the SuperKEKB energy-asymmetric $e^+ e^-$ collider is a substantial
upgrade of the B factory facility at KEK in Tsukuba, Japan. It aims to record a factor of 50 times
more data than its predecessor. The experiment completed a commissioning run in 2018, and
began full operation in early 2019. Belle II is uniquely capable of studying the so-called "XYZ"
particles: heavy exotic hadrons consisting of more than three quarks. First discovered by Belle,
these now number in the dozens, and represent the emergence of a new category within quantum
chromodynamics. This talk will present the prospects of Belle II to explore both exotic and
conventional quarkonium physics.
The discovery of pentaquark candidates in Lb->JpsipK decays at LHCb has opened a new field in exotic spectroscopy. Analysis of full dataset of b-hadron decays collected during Run I and II provides opportunities to examine the established states with better precision, their investigation in new decay modes and for searches of new exotic hadron candidates. Recent results of these studies will be presented.
A statistical combination of the search results for the X(5568) resonance decaying into $B_s π$ is reported, based on published results from the ATLAS, CMS, CDF and LHCb Collaborations.
A narrow structure in the invariant mass distribution of $B^0_s π^±$ has been observed by the D0 Collaboration with a mass value of 5568 MeV but not confirmed by any of the latest searches from the other Collaborations.
CDF and the LHC experiments have set limits on $ρ_X$, the relative production rate of the X(5568) and $B^0_s$ states times the branching ratio for the $X(5568)\rightarrow B^0_s π^±$ decay.
By applying a statistical combination of limits set by the three LHC experiments, we derive a limit, at 95% Confidence Level, of $ρ_X$ < 0.92% for $p_T(B^0_s)$ > 10 GeV, and $ρ_X$ < 0.91% for $p_T(B^0_s )$ > 15 GeV, which represent the most stringent upper limits up to present.
The talk will review the experimental results from Tevatron and LHC, will describe the combination procedure and the obtained results. The effect of including the results from Tevatron experiments in the statistical combination will also be discussed.
Jets, clusters of collimated particles, produced from parton scatterings in high energy
proton-proton collisions are an effective tool to study the internal proton structure. At center of mass
energies of $\sqrt{s} = $ 200 and 510 GeV, jet production is dominated by the quark-gluon, $qg$ and
gluon-gluon, $gg$, scattering processes. The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) has measured a series of jet asymmetries in the pseudo-rapidity range, $-1 < \eta < 2$, in longitudinally polarized $pp$ collisions to constrain the gluon polarization in the proton. Similarly jet cross-section measurements for unpolarized $pp$ collisions are an excellent probe to constrain the unpolarized gluon distribution. In this talk the STAR jet cross-section measurements in two $\eta$ ranges, $ |\eta| < 0.5$ and $ 0.5 < |\eta| < 0.9$ for $510$ GeV $pp$ data are presented. The techniques used in this analysis, such as the underlying event correction to the jet energy and the unfolding procedure that maps the detector-level jet quantities to physics quantities at the particle level are described. Their impact on the unpolarized proton parton distribution functions through re-weighting is discussed.
Jet measurements play an essential role in PDF fits and the available measurements will be briefly summarized. The primary experimental uncertainties in these measurements are the knowledge of the jet energy scale and resolution. The analyses used to evaluate these uncertainties will be described as well as how they are combined to form the set of uncertainties that dominate these measurements. How these uncertainties should be correlated between ATLAS measurements and those of other experiments in PDF fits will be discussed too. Estimated projections towards higher luminosity will also be briefly discussed.
We present fits to determine parton distribution functions (PDFs) using inclusive W/Z-boson and W+jets measurements from the ATLAS experiment at the LHC. The ATLAS measurements are used in combination with deep-inelastic scattering data from HERA. If available, we also present the results of PDF fits that use Z+jets measurements from ATLAS in addition to the measurements listed above. The ATLAS W and Z boson data exhibit sensitivity to the valence quark distributions and the light quark sea composition. The parton distribution functions extracted using W+jets data show an improved determination of the high-x sea-quark densities, while confirming the unsuppressed strange-quark density at lower x<0.02 found by previous ATLAS analyses.
The associated production of vector bosons V (W, Z or gamma) and jets originating from heavy-flavour (c or b) quarks is a large background source in measurements of other standard model processes, Higgs boson studies, and many searches for physics beyond the SM. The study of events with a vector boson accompanied by heavy-flavour jets is crucial to refine the theoretical calculations in perturbative QCD, as well as to validate associated Monte Carlo predictions. Differential cross sections in V+ c/b jets are measured as a function of several kinematic observables with the CMS detector at 8 and 13 TeV. The study of the associated production of a vector boson with jets from a c-quark is especially interesting, as it allows to extract information on the proton parton density functions.
Jet production measurements have represented one of the cornerstones of global PDF analyses since the early days of the Tevatron. Here we critically revisit the impact of jet production measurements from the LHC at 7 and 8 TeV within a global PDF fit by exploiting recent progress in NNLO QCD calculations. For the first time, we demonstrate that dijet production measurements can be successfully included within a NNLO global PDF fit and quantify the information that they provide on the large-x gluon. We compare the PDF impact of inclusive jet measurements from those provided by the dijet data, and assess in both cases the perturbative convergence of the theoretical predictions and the role of the choice of renormalisation and factorisation scale. We also assess the stability if our results with the choice for the correlation model used to construct the experimental covariance matrices.
Latest results about searches for new resonances with the CMS experiment will be presented. Prospects for Run III and beyond will be also discussed.
Many extensions to the Standard Model predicts new particles decaying into two bosons (W, Z, photon, or Higgs bosons) making these important signatures in the search for new physics. Searches for such diboson resonances have been performed in final states with different numbers of leptons, photons and jets and b-jets where new jet substructure techniques to disentangle the hadronic decay products in highly boosted configuration are being used. This talk summarizes recent ATLAS searches for diboson resonances in VV, VH and HH final states with the full Run2 LHC data.
Many theories beyond the Standard Model (BSM) predict new
phenomena at the highest energies accessible by the LHC. These often give rise to heavy resonances consisting of either isolated high-pt leptons or pairs of jets, either exclusively or in conjunction with other objects. Alternatively, should new physics be beyond the scale of the LHC, non-resonant signatures in these final states can provide an indirect probe beyond the centre of mass energy. The talk will focus on the most recent full Run 2 results using 13 TeV pp collision data.
Since the discovery of the Higgs boson with the mass of about 125 GeV much effort has been spent looking for further scalars, which are motivated in many scenarios. Here we report on searches for new neutral heavy Higgs bosons decaying to pairs of third generation fermions: tau leptons or b quarks. These searches are based on full Run2 data of the ATLAS experiment at the LHC.
The Election-Ion Collider (EIC) is a next generation accelerator, which is designed to answer longstanding questions in nuclear physics. The EIC with its wide range of center of mass energies from 20 to 140 GeV, polarized beams, and beam species, as well as high luminosity, is designed to precisely image the quarks and gluons and their interactions, and to explore the new QCD frontier of strong color fields in nuclei, in short, to understand how matter at its most fundamental level is made. Many nuclear effects of interest at an EIC depend on the geometry of the collision, e.g., the free path length, the impact parameter, and the nuclear thickness that is probed by the photon in the interaction. In this work, a systematic investigation of the collision geometry using the detection of neutrons emitted under small angles is presented. The study is based on the BeAGLE event generator, which is a hybrid model of combining Pythia-6, DPMJet, and Fluka for simulating the deep inelastic scattering process of electron-ion collisions. Studies to tune the Monte Carlo model in BeAGLE on existing data and to determine the detector requirements of a Zero-Degree-Calorimeter (ZDC) will be presented.
A technique has been recently proposed to address the main limitations of past neutrino scattering experiments. In particular, it allows precise measurements of high statistics samples of (anti)neutrino-hydrogen interactions and of various nuclear targets. The planned high intensity LBNF beams give access to a broad mixture of measurements of electroweak parameters, QCD and hadron structure of nucleons and nuclei, nuclear physics, form factors, structure functions and cross-sections, as well as searches for new physics or verification of existing outstanding inconsistencies.
The LHeC and the FCC-eh will open a new realm in our understanding of nuclear structure and the dynamics in processes involving nuclei, in an unexplored kinematic domain. In this talk we will review the most recent studies as shown in the update of the 2012 CDR recently delivered. We will discuss the determination of nuclear parton densities in the framework of global fits and for a single nucleus. Then we will discuss diffraction, both inclusive and exclusive. Finally we will demonstrate the unique capability of these high-energy colliders for proving the long sought non-linear regime of QCD, saturation, to exist (or to disprove). This is enabled through the simultaneous measurements, of similar high precision and range, of ep and eA collisions which will eventually disentangle non-linear parton-parton interactions from nuclear environment effects.
The LHeC and the FCC-eh offer fascinating, unique possibilities for discovering BSM physics in DIS, both due to their large centre-of-mass energies and high luminosities. In this talk we will review most recent studies as presented in the 2020 LHeC White Paper. We will show the prospects for observing extensions of the Higgs sectors both with charged and neutral scalars, anomalous Higgs couplings and exotic decays. Then we will discuss searches for R-parity conserving and violating supersymmetry both with prompt and long-lived particles, and of feeble interacting particles like sterile neutrinos, fermion triplets, dark photons and axion-like particles. Finally we will address anomalous couplings and searches for heavy resonances like leptoquarks and vector-like quarks, excited fermions and colour-octet leptons.
We present the use of machine learning to reconstruct deep inelastic scattering (DIS) kinematics. In particular, we trained deep neural networks to reconstruct $x$ and $Q^2$ based on information from the lepton and the hadronic system in $e^{\pm}p$ scattering at the ZEUS experiment at HERA. These models were trained by a careful selection of Monte Carlo events. The results from the neural networks were compared to those of classical reconstruction methods, including the electron method, the Jacquet-Blondel Method, and the double-angle method. The classical methods considered can provide a good reconstruction of DIS kinematics; however, by only considering partial information from an event, each method has its limitations, including a sensitivity to initial and final state QED radiation, a requirement of precise energy measurements, and/or a poor resolution on different kinematic regions. The neural networks trained in our study reconstruct event kinematics based on the information used in the classical methods, but, in addition, are enhanced through correlations and patterns revealed in the simulated data sets from event generators. We show that, with the appropriate selection of a training set, data enhances the neural networks sufficiently to outperform all classical reconstruction methods on most of the kinematic range considered. The availability of large amounts of Monte Carlo events, and the ability of neural networks to effectively extract information from large data sets, both suggest that a neural network reconstruction of DIS kinematics can serve as a rigorous method to combine and outperform the classical reconstruction methods.
The associated production of vector boson with quarkonia is a key observable for understanding the quarkonium production mechanisms, including the separation of single and double parton scattering components.
This talk will present the latest measurements from ATLAS on quarkonium production, including associated production, and recent results from heavy flavour production. In addition, recent searches for exotic states, such as pentaquarks, will be highlighted.
The heavy quarkonium together with b-hadrons provide a rich material for testing effective theories of strong interaction via production, decay and spectroscopy studies. This talk presents recent progress on these studies at LHCb obtained using the full dataset collected during runs I and II of the LHC.
The ATLAS experiment has performed accurate measurements of mixing and CP violation in the neutral B mesons, and also of rare processes happening in electroweak FCNC-suppressed neutral B-mesons decays.
This talk will focus on the latest results from ATLAS, such as rare processes: B^0_s → mu mu and B^0 → mu mu; and CPV in Bs to Jpsi Phi, where Standard Model predicts the CP violating phase, phi_s, to be very small and is very well constrained, while in many new physics models large phi_s values are expected. The Bs0→J/psi phi decay channel is sensitive to the new physics contributions, and already small deviations in a measurement of phi_s would be hints for the existence of the new particles.
The Belle II experiment at the SuperKEKB energy-asymmetric $e^+ e^-$ collider is a substantial upgrade of the B factory facility at the Japanese KEK laboratory. The design luminosity of the machine is $8\times 10^{35}$ cm$^{-2}$s$^{-1}$ and the Belle II experiment aims to record 50 ab$^{-1}$ of data, a factor of 50 more than its predecessor. With this data set, Belle II will be able to measure the Cabibbo-Kobayashi-Maskawa (CKM) matrix, the matrix elements and their phases, with unprecedented precision and explore flavor physics with $B$ and charmed mesons, and $\tau$ leptons. Belle II has also a unique capability to search for low mass dark matter and low mass mediators. We also expect exciting results in quarkonium physics with Belle II. In this presentation, we will review the status of the Belle II detector, the results of the planned measurements with data collected in 2019, and the prospects for physics at Belle II.
In the Color Glass Condensate effective theory framework, the evolution of high energy scattering amplitudes with collision energy is given by thy Balitsky-Kovchegov (BK) equation. It is usually derived from the JIMWLK hierarchy in the in the large-Nc limit. The next-to-leading order evolution equation for the 2-point correlator, related to the total deep inelastic scattering cross section, involves 6-point correlators of Wilson lines. We present a fully analytic calculation of these correlators in the finite Nc case, using the Gaussian Truncation approximation. We use these results to find the relative importance of finite Nc corrections to the next-to-leading order evolution equation. We show numerically that the finite Nc corrections are negligible, as expected.
We present the first computation of the next-to-leading order (NLO) photon+dijet impact factor in e+A DIS at small $x$ in the framework of the Color Glass Condensate (CGC) effective field theory. When combined with the recent derivation of JIMWLK small $x$ evolution to next-to-leading logarithm (in $x$) accuracy, this result provides us with a prediction of the photon+dijet cross-section in e+A DIS to O($\alpha_S^3 \ln(1/x)$) accuracy. In the soft photon limit, the Low-Burnett-Kroll soft photon theorem allows us to obtain the first CGC results for inclusive dijet production up to the same accuracy. The comparison of these results with dijet and photon+dijet measurements at a future Electron Ion Collider (EIC) therefore provides a precision test of the systematics of gluon saturation. A remarkable simplification is brought about by the use of momentum space ``dressed'' quark and gluon propagators in the light cone gauge $A^{-}=0$ which facilitates the extension of our computational techniques to higher loop orders.
Deep Inelastic Scattering (DIS) is the cleanest tool available to probe the content of a fast proton or nucleus. In the regime of low Bjorken x, one enters in the nonlinear regime of gluon saturation, where the gluons are better described within the framework of Color Glass Condensate (CGC) and the dipole factorization. This framework allows to resum coherent multiple scattering on the target, and also to resum the high-energy leading logarithms (LL).
So far, phenomenological studies have been performed successfully at LO + LL resummation in the dipole factorization using HERA data for proton DIS. However, in order to reach precision, NLO corrections with massive quarks (which is known to be sizable in DIS at NLO) should be included as well as high-energy NLL resummations. This is important not only to extract as much knowledge as possible out of the HERA data, but also in prevision of future electron-proton and/or electron-nucleus colliders.
In this talk, we will discuss the calculation of the massive quark contribution to the NLO corrections to DIS structure functions on a dense target in the dipole factorization picture. In particular, we will present the complete result for the longitudinal structure function at NLO including massive quarks in that setup.
The agreement between calculations inspired by the resummation of energy logarithms, known as BFKL approach, and experimental data in the semi-hard sector of QCD has become manifest after a wealthy series of phenomenological analyses. However, the contingency that the same data could be concurrently portrayed at the hand of fixed-order, DGLAP-based calculations, has been pointed out recently, but not yet punctually addressed.
We make use of disjoint intervals for the transverse momenta of the emitted objects in the final state, i.e. $\kappa$-windows, to clearly highlight how high-energy resummed and fixed-order driven predictions for semi-hard sensitive observables in di-jet and hadron-jet production channels can be decisively discriminated in the kinematic ranges typical of current and forthcoming analyses at the LHC.
We perform analysis of the pole structure of the BFKL eigenvalues in Mellin space with different forms of the kinematical constraint imposed on the low x evolution. We find that all of them generate the same leading anti-collinear poles which agree with BFKL up to NLL order and up to NNLL in N=4 sYM. The coefficients of subleading poles vanish up to NNLL order for all constraints and we prove that this property should be satisfied to all orders. We demonstrate that further subleading poles generated by kinematical constraints differ from the NLL and NNLL results. We quantify the differences between the different forms of the constraints by performing numerical analysis both in Mellin space and in momentum space.
Recent experimental measurement of deeply virtual Compton scattering off the neutron by Hall A JLab collaboration [Benali et al., Nat. Phys. 16, 191 (2020)] provides welcome addition to the endeavor of determination of nucleon GPDs. This should be an important step towards both determination of elusive GPD E and flavor decomposition of DVCS amplitude. We will describe repercussions of this data on global DVCS fits.
Using a recent extraction of deeply virtual Compton scattering (DVCS) Compton form factors, done within the PARTONS framework, we derive timelike Compton scattering (TCS) amplitudes and calculate TCS observables only assuming leading-twist dominance. In the framework of collinear QCD factorization, the leading-twist scattering amplitudes for DVCS and TCS are intimately related thanks to analytic properties of leading and next-to-leading order amplitudes. We exploit this welcome feature to make data-driven predictions for TCS observables to be measured in near future experiments. Artificial neural network techniques are used for an essential reduction of model dependency, allowing for stringent tests of the universality of leading-twist description of DVCS and TCS amplitudes in terms of Generalized Parton Distributions (GPDs). Moreover, this study helps to understand quantitatively the complementarity of DVCS and TCS measurements, which is crucial e.g. to perform the nucleon tomography.
Ioffe time essentially quantifies the distance along the lightcone that the quark fields that enter the correlator describing the Parton Distribution Function (PDF) are separated by. In this sense, it is a natural candidate for clearly separating the short distance physics from the long distance physics. We study how the behavior of the psrton distribution in Ioffe time can be mapped out given its Mellin moments and a Regge fit parameter. Pseudo PDFs describe nucleon matrix elements of quark field operators separated by a space like distance $z$. These are calculable in lattice QCD and as $z^2$ approaches zero, pseudo PDFs approach the actual PDFs. Complimentary to the lattice efforts, we study the behavior pseudo PDFs as a function of $z^2$ in a diquark model. We also extend the study to pseudo Generalized Parton Distributions (GPDs) which essentially involves taking into account an extra degree of freedom because of the non diagonal nature of the hadronic matrix element in the case of GPDs.
We study the relative importance of double Bethe-Heitler, single Bethe-Heitler and QCD processes in the electroproduction of two photons with a large invariant mass, for both JLab and EIC kinematics.
The form factors of the energy-momentum tensor (EMT) contain a wealth of information about the nucleon. At the density level, this information can be described in terms of energy, pressure, shear forces and angular momentum distributions inside the nucleon. In this talk we present recent results on the associated 2D densities of the energy-momentum tensor in the bag model, formulated in the large-$N_c$ limit. We also study the properties of the 2D EMT densities of the nucleon in a non-relativistic limit and in the heavy quark limit.
Proton parton distribution functions (PDFs) are poorly constrained by existing data for Bjorken $x$ larger than 0.6, and the PDFs extracted from global fits differ considerably from each other. A technique for comparing predictions based on different PDF sets to observed event numbers is presented. It is applied to compare predictions from the most commonly used PDFs to published ZEUS data at high Bjorken $x$. A wide variation is found in the ability of the PDFs to predict the observed results. A scheme for including the ZEUS high-$x$ data in future PDF extractions is discussed.
The CJ15 global next-to-leading-order analysis of PDFs utilized, amongst others, inclusive and tagged DIS structure function data from Jefferson Lab (JLab) and high-precision charged lepton and W-boson asymmetry data from Fermilab. As an extension to the CJ15 analysis, new JLab Hall A and C data from experiments jl00106F2, e06009d, e99118, jlcee96 and e03103, and Hall B data from the BONuS and CLAS6 experiments are included to determine their impact on the extraction of PDFs at intermediate and high x, as well as on the nuclear corrections in the deuteron. Preliminary results will be presented in this talk.
Using data from a recent reanalysis of neutron structure functions extracted from inclusive proton and deuteron DIS, we re-examine the constraints on the shape of the $\bar d − \bar u$ asymmetry in the proton at large parton momentum fractions $x$. A global analysis of the proton–neutron structure function difference from BCDMS, NMC, SLAC and Jefferson Lab DIS measurements, and of Fermilab Drell-Yan lepton-pair production cross sections, suggests that existing data can be well described with $\bar d > \bar u$ for all values of $x$ currently accessible. We compare the shape of the fitted $\bar d − \bar u$ distributions with expectations from nonperturbative models based on chiral symmetry breaking, and assess the impact of new data from the SeaQuest experiment at larger values of $x$.
We formulate a general approach to the inclusion of theoretical uncertainties, specifically those related to the missing higher order uncertainty (MHOU), in the determination of parton distribution functions (PDFs). We demonstrate how, under quite generic assumptions, theory uncertainties can be included as an extra contribution to the covariance matrix when determining PDFs from data. We define a set of prescriptions for constructing a theory covariance matrix using scale variations, which can be used in global fits of data from a wide range of different processes, based on choosing a set of independent scale variations suitably correlated within and across processes. We peform a NLO PDF determination which includes the MHOU, assess the impact of the inclusion of MHOUs on the PDF central values and uncertainties, and validate the results by comparison to the known shift between NLO and NNLO PDFs. We finally study the impact of the inclusion of MHOUs in a global PDF determination on LHC cross-sections.
We present a new, simultaneous extraction of spin-averaged and spin-dependent PDFs within a multi-step Monte Carlo analysis. Utilizing data from inclusive jet production in unpolarized and polarized proton-proton and proton-antiproton collisions, we determine for the first time the spin-dependent gluon distribution, $\Delta g(x)$, at the same time as the unpolarized gluon PDF, $g(x)$. Preliminary results from the first combined unpolarized + polarized global QCD analysis will be presented.
We present a comprehensive review of existing Monte Carlo methods used in global QCD analyses of parton distribution functions. We critically examine the interpretability of uncertainties on extracted parton distributions against nested sampling and the more traditional Hessian approach. We show how in some cases the inclusion of resampling, partition, and cross-validation of the data can inflate uncertainties on the fitted distributions, and formulate criteria to assess incompatibilities of data sets included in a fit.
Experimental measurements of Drell-Yan (DY) vector-boson production
are available from the Large Hadron Collider (LHC) and from lower-energy collider and fixed-target experiments. In the low transverse momentum end of DY spectra, important for the extraction of the $W$-boson mass at the LHC, QCD contributions from non-perturbative Sudakov form factors and intrinsic transverse momentum become relevant. We study the potential for determining such contributions from fits to LHC and lower-energy experimental data, using the framework of low-$q_T$ factorization for differential DY cross sections in terms of transverse momentum dependent (TMD) distribution functions. We investigate correlations between different sources of TMD non-perturbative effects, and correlations with collinear parton distributions. We stress the relevance of accurate low-mass DY measurements with fine binning in transverse momentum for improved determinations of long-distance contributions to Sudakov evolution processes and TMDs.
Precision measurements of the production cross-sections of W/Z boson at LHC provide important tests of perturbative QCD and information about the parton distribution functions for quarks within the proton. We present measurements of fiducial integrated and differential cross sections for inclusive W+, W− and Z boson production using data collected by the ATLAS experiment at center-of-mass energies of 2.76 and 8 TeV. Measurements of the transverse momentum distribution of Drell-Yan lepton pairs at 13 TeV are also presented. The measurements are corrected for detector inefficiency and resolution and compared with state-of-the-art theoretical calculations.
The study of the associated production of vector bosons and jets constitutes an excellent testbench to check numerous QCD predictions. Total and differential cross sections of vector bosons produced in association with jets have been studied in pp collisions at 7, 8 and 13 TeV center-of-mass energies. Differential distributions as function of a broad range of kinematical observables are measured and compared with theoretical predictions. Final states with a vector boson and jets can be also used to study electroweak initiated processes, such as the vector boson fusion production of a Z or W boson that are accompanied by a pair of energetic jets with large invariant mass.
In this talk, I am going to introduce our recent works about TMD factorization and resummation for Z boson tagged jets production at the LHC, which can be used to study the proton TMD structure and QCD factorization violation effects. We investigated jet production with the standard jet axis and also the winner-take-all axis. In the first case, we derived an all-order factorization formula, which allows for the systematic resummation of all large logarithms, including small-R and non-global logarithms(NGLs). In the second case, we find that the azimuthal angle decorelation is insensitive NGLs, and we resum all large logs at the NNLL level. The corresponding references are 2003.XXXXX, 1905.01335, 1901.09038.
Investigating the three-dimensional structure of the nucleon has been an active field of research, especially so since the introduction of the generalized parton distributions (GPD). Research focused on this three-dimensional structure continues to be central to the hadron physics program at facilities like Jefferson Lab. The GPD formalism provides a unified description of many important reactions including elastic electron scattering, deep-inelastic scattering, deeply-virtual and Timelike Compton Scattering (DVCS and TCS), deeply-virtual meson production (DVMP), and wide-angle real Compton scattering (RCS) and meson production. To extract the rich information on nucleon structure encoded in GPDs one needs to show that the scattering process is understood. The kinematic dependencies of the basic longitudinal-transverse separated cross section is the only unambiguous way to do that. The Hall C focusing spectrometers with large momentum reach, rigid connection to a sturdy pivot, well-reproducible magnetic properties, provide the facilities for the validation of the exclusive reaction process and crucial insight into imaging nucleon structure. The two-arm combination of the new high-resolution neutral-particle spectrometer (NPS) and the Hall C focusing spectrometers extends these scientific capabilities to exclusive reactions with neutral final states. The NPS enables precision measurements of the DVCS cross section at different beam energies to extract the real part of the Compton form factor without any assumptions and pushes the energy scale of RCS, the process of choice to explore factorization in a whole class of wide-angle processes and its extension to neutral pion photo-production. It makes possible to validate QCD factorization, a cornerstone of 3D transverse momentum imaging, by measurements of the basic semi-inclusive neutral-pion cross section. Much progress in imaging nucleon structure can be made with electron-scattering reactions, yet experiments utilizing high-energy photons play a unique complementary role. Measurements involving the small scattering probabilities associated with these exclusive reactions demand high-intensity photon beams. The combination of high precision calorimetry of the NPS and a novel compact high intensity photon sources (CPS) greatly enhances scientific benefit to exclusive processes like RCS and TCS with transverse polarized targets. It offers a gain in scientific production of a factor of 30 as compared to existing such techniques. I will describe the unique science program in Hall C as enabled by the NPS and CPS.
The muonic-deuterium spectroscopic measurements obtained a significantly smaller (5.6 $\sigma$) deuterium charge radius as compared to the CODATA 2014 value. It is also 2.6 $\sigma$ away from the combined value of the proton charge radius from the muonic-hydrogen measurements and the isotope shift value from ordinary hydrogen and deuterium measurements, indicating an effect from the neutron charge distribution. Such a puzzling discovery awaits further precision investigations with different experimental techniques, and thus the DRad experiment (Jefferson Lab PR12-17-009) was proposed to measure the $e-d$ elastic scattering cross-sections with low momentum transfers ($\rm{Q}^2 = 2\times10^{-4} - 5\times10^{-2}~\rm{(GeV/c)}^2$), and precisely extract the deuterium charge radius. The designed setup of this experiment is largely based on that of the PRad experiment (Jefferson Lab E12-11-106), but with a low energy Si-based cylindrical recoil detector in the windowless target cell to reject the inelastic background. The design also includes an additional Gas Electron Multiplier (GEM), which improves the tracking capability and hence reduces the beam-line background and related systematic uncertainties. The measured $e-d$ cross-sections will be normalized to the well-known M$\o$ller process, which can be measured simultaneously with a similar kinematic range and detector acceptance. In this talk, we will present the DRad experimental setup and its projections.
Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with an additional electron ring. The proposed collider will provide highly polarized electrons (with the polarization ~80%), protons and Helium-3 (both with the polarization ~70%), as well as unpolarized ion beams from Carbon to Uranium with viable center of mass energy from 10 to 20 GeV and the luminosity of (2 ~ 4) × 10$^{33}$ cm$^{−2}$∙s$^{−1}$.
The main foci of the EicC will be the precision measurements of the structure of proton in the sea quark region, including 3D tomography of nucleon which reveals the QCD dynamics; the partonic structure of nuclei and the parton interaction with the nuclear environment, in particular, the short range correlation of nucleons and the cold nuclear matter effects; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with the cutting-edge technology.
In this talk, the physics program, detector conceptual design and the project status will be reported.
The internal structure of the Nucleon has been studied for more than 60 years providing a very good understanding of its dynamics. On the other hand, the internal structure of the pion, which is in principle the simplest QCD bound state, is less explored, and its Parton distribution functions less known. Nevertheless, the presence of a virtual meson-cloud surrounding the Nucleon has been successful to explain the deviation of the Gottfried sum rule and implying the possibility of using the cloud as a virtual target, thus accessing pion structure through the Sullivan process (electron scattering off the nucleon meson cloud). Making use of the tagging technique (measuring one or more of the recoil nucleons in coincidence with the scatter electron) allows to isolate the Sullivan process from competing reactions.
The Tagged Deep Inelastic Scattering (TDIS) experiment at Hall A at the Jefferson Laboratory will make use of the Sullivan process to access the pion structure function, tagging the leading nucleon of the reaction with a new state-of-the-art multi time projection chamber in conjunction with the new Super Bigbite Spectrometer for electron detection. This talk will present the motivation and present status of the experiment.
PHENIX has made a comprehensive measurement of low p$_\mathrm{T}$ direct photon yield in Au+Au collisions at 200 GeV that show both a large yield and a large azimuthal anisotropy produced. The mechanism for such simultaneous large production is not well understood yet.
Recently the PHENIX collaboration has improved on those measurements by using the Au+Au data collected in 2014 which provides a 10-fold increase in statistics. Furthermore, PHENIX has found that the low p$_\mathrm{T}$ direct photon yield dN$_{\gamma}$/d$\eta$ is proportional to (dN$_\mathrm{ch}$/d$\eta$)$^\alpha$. This scaling holds for beam energies both at RHIC and at the LHC in large-on-large systems. An extrapolation to smaller systems suggests an onset of QGP formation at low dN$_\mathrm{ch}$/d$\eta$.
In this talk I will show the most recent results on direct photon measurements from large and small systems.
Photon-induced processes in proton-proton interactions have become recently very topical. The large energy at the LHC, when combined with relatively large luminosity at run II, allows to start the exploration of such processes.
We discuss production of $W^+ W^-$ pairs and $t \bar t$ quark-antiquark pairs in proton-proton collisions induced by two-photon fusion including, for a first time, transverse momenta of incoming photons. The unintegrated inelastic fluxes (related to proton dissociation) of photons are calculated based on modern parametrizations of deep inelastic structure functions in a broad range of $x$ and $Q^2$.
We focus on processes with single and double proton dissociation. Highly excited remnant systems hadronise producing particles that can be vetoed in the calorimeter. We calculate associated effective gap survival factors. The gap survival factors depend on the process, mass of the remnant system and collision energy. The rapidity gap survival factor due to remnant fragmentation for double dissociative (DD) collisions is smaller than that for single dissociative (SD) process. We observe approximate factorisation: $S_{R,DD} \approx S_{R,SD}^2$ when imposing rapidity veto. For the $W^+W^-$ final state, the remnant fragmentation leads to a taming of the cross section when the rapidity gap requirement is imposed. Also for $t \bar t$ quark-antiquark pairs such a condition reverses the hierarchy observed for the case when such condition is taken into account. Our results imply that for the production of such heavy objects as $t$ quark and $\bar t$ antiquark the virtuality of the photons attached to the dissociative system are very large ($Q^2 <$ 10$^{4}$ GeV$^2$). A similar effect was observed for the $W^+ W^-$ system.
A. SHABETAI (for the ALICE Collaboration)
Highly energetic point-like partons produced in a hard scattering will lead to a parton shower which will be fragmenting into a hadronic spray of particles called a jet. The partonic stage of such shower can be calculated from first principles using the QCD factorisation theorem. Jet substructure observables, such as jet fragmentation functions and groomed observables, provide an ideal tool to test perturbative QCD.
Jets are produced in the early stage of ultrarelativistic heavy-ion collisions. They can thus be used to probe the Quark-Gluon Plasma. The interaction of the virtual parton shower with the medium is known as jet quenching. This is a complex process in which quantum interference plays a fundamental role and leads to multiple consequences occurring at the same time:
- The re-distribution of the jet energy which is transported to large angles relative to the jet axis
- The modification of jet structure
- Jet deflection (which can be defined as an opening angle in a di-jet system) also known as accoplanarity which distribution is becoming broader.
Ultimately a consistent picture must emerge from measuring all those aspects, since they are all driven by the same underlying physical processes.
The central barrel of the ALICE detector at the LHC has unique tracking capabilities enabling to measure charged particles down to transverse momenta ($p_\mathrm{T}$) as low as 150 MeV/$c$ and provides particle identification. Combining information from the ALICE Time Projection Chamber and from the Electromagnetic Calorimeters EMCal/DCal allows precise measurements of the jet energy. Due to recent advances in jet finding techniques, measurements of inclusive or recoil jets with large resolution parameters are now experimentally accessible, via semi-inclusive hadron-jet or machine learning techniques down to low jet $p_\mathrm{T}$.
We will discuss a variety of recent measurements in pp and p-Pb and Pb-Pb collision by the ALICE collaboration. Including detailed studies of the parton shower through observables like the jet mass, jet fragmentation functions and jet substructure observables or nuclear modification factors, as well as searches for the broadening of the accoplanarity distribution (measured by the semi-inclusive distribution of jets recoiling from a high-$p_\mathrm{T}$ hadron) and the first direct measurement of the dead-cone effect at colliders using iterative jet declustering techniques.
Heavy flavor production is an ideal tool to study the properties of the QCD medium created at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The kinematic coverage and production mechanisms of the heavy flavor are different between RHIC and LHC. The PHENIX experiment has a comprehensive physics program which studies open heavy flavor and quarkonium production in relativistic heavy-ion collisions. It is critical to measure both open heavy flavor and quarkonium in different collision systems to disentangle cold (initial state) and hot nuclear medium (final) effects. The heavy quarks (charm and beauty) are predominantly produced in the early stage of the collisions via hard partonic scattering processes. Therefore, they experience the full evolution of the nuclear medium.
The recent PHENIX results on heavy flavor and quarkonium production measured in p+p, p+Al, p+Au, He+Au, and Au+Au collisions as a function of centrality, rapidity, and transverse momentum will be presented, and interpretation of the results with respect to the current theoretical understanding will be discussed in this talk.
Deep inelastic scattering (DIS) total cross section data at small-x as measured by the HERA experiments is well described by Balitsky-Kovchegov (BK) evolution in the leading order dipole picture [1-3]. Recently the full Next-to-Leading Order (NLO) dipole picture total cross sections have become available for DIS [4-6], and a working factorization scheme has been deviced which substracts the soft gluon divergence present at NLO [7].
We report our ongoing work in which we make the first comparisons of the NLO DIS total cross sections to HERA data. The non-perturbative initial condition to BK evolution is fixed by fitting the HERA reduced cross section data. As the NLO results for the DIS total cross section are currently available only in the massless quark limit, we also fit a light quark only cross section constructed with a parametrization of published total and heavy quark data. We find an excellent description of the HERA data. Since the full NLO BK equation is computationally expensive [8], we use a number of beyond LO prescriptions for the evolution that include most important higher order corrections enhanced by large transverse logarithms, including the recent version of the equation formulated in terms of the target rapidity [9].
[1] T. Lappi, H. Mäntysaari, Phys.Rev. D88 (2013) 114020
[2] E. Iancu, J.D. Madrigal, A.H. Mueller, G. Soyez, D.N. Triantafyllopoulos, Phys.Lett. B750 (2015) 643-652
[3] B. Ducloué, E. Iancu, G. Soyez, D.N. Triantafyllopoulos, arXiv:1912.09196 [hep-ph]
[4] G. Beuf, Phys.Rev. D94 (2016) no.5, 054016
[5] G. Beuf, Phys.Rev. D96 (2017) no.7, 074033
[6] H. Hänninen, T. Lappi, R. Paatelainen, arXiv:1711.08207 [hep-ph]
[7] B. Ducloué, H. Hänninen, T. Lappi, Y. Zhu, Phys.Rev. D96 (2017) no.9, 094017
[8] T. Lappi, H. Mäntysaari, Phys.Rev. D91 (2015) no.7, 074016
[9] B. Ducloué, E. Iancu, A.H. Mueller, G. Soyez, D.N. Triantafyllopoulos, JHEP 1904 (2019) 081
Using the formalism of the light-cone wave function in pQCD together with the hybrid factorization, we compute the cross-section for two and three particle production at forward rapidities in proton-nucleus collisions. We focus on the quark channel, in which the three produced partons -- a quark accompanied by a gluon pair, or two quarks plus one antiquark -- are all generated via two successive splittings starting with a quark that was originally collinear with the proton. The produced partons are put on-shell by their scattering off the nuclear target, described as a Lorentz-contracted "shockwave". By using the three-parton component of the quark light-cone wave function, together with the virtual corrections, we can then present our progress on the computation of the next-to-leading order correction to the cross-section for the production of a pair of jets.
We present the computation of exclusive and inclusive dijet production in electron-proton and electron-nucleus collisions at small-x within the Color Glass Condensate effective field theory. We compute the cross-sections differentially in mean dijet momentum and momentum imbalance, as well as its corresponding elliptic anisotropy. For exclusive dijet production, we employ a dipole model with impact parameter and orientation dependence from a modified McLerran-Venugopalan model that incorporates the finite-size charge density of the target. For inclusive dijet production, we confirm and extend existing results in the correlation limit approximation by computing the differential cross-section and elliptic anisotropies from full multi-gluon correlations using the Gaussian approximation of high energy correlators, and Balitsky-Kovchegov evolution with running coupling. For both exclusive and inclusive production, we highlight kinematical regions for observing potential signals of saturation and measuring multi-gluon correlations in a future Electron-Ion Collider.
In the search for a clear signal of underlining BFKL dynamics in high-energy diffractive processes the Mueller-Tang jet observables have been proven to be a particularly fortunate choice.
Despite unavoidable unperturbative effects that can affect the rapidity gap signature good agreement was found between the BFKL predictions and the Tevatron data.
The extent of the agreement was partially unexpected considering the modest energy available and the incomplete refinement of the BFKL predictions.
On the experimental side it is clear that the higher LHC energy promise a further BFKL enhancement while, as for the theoretical analysis, the obvious path forward is to complete the NLO predictions incorporating also the most recently calculated piece, the NLO vertex.
The inclusion of the NLO vertex passes through the implementation of the momentum space BFKL eigenfunctions, which represent a novelty in this context, and introduce several technical complications that hinder the theoretical analysis.
We present progresses toward this goal, explaining the origin of such complications and the chosen solutions.
We present progress toward the theoretical understanding of BFKL effects in dijet processes in order to better isolate kinematical regimes relevant to
experiments. BFKL effects have been notoriously difficult to clearly identify in processes involving two jets. The theoretically simplest example, Mueller-Navelet or inclusive dijets, has been shown to be well described via DGLAP evolution. We describe progress in identifying new observables that more strongly depend on BFKL effects that might show clear signatures at the LHC. The cleanest experimental example is that of Mueller-Tang jets. Here dijets are produced with a large rapidity gap resulting from single Pomeron exchange. Theoretically this requires a more complicated description, but recent progress in understanding the combination of the NLL kernel and the NLO impact factors have made a theoretical prediction possibly that is consistent with current results from the LHC. For the first time all the NLO terms were taken into account in the analysis.
A study of events where the two leading jets are separated by a large pseudorapidity interval void of particle activity, known as jet-gap-jet events, is presented. The jets have transverse momentum pT, jet > 40 GeV and pseudorapidity 1.4 < | ηjet | < 4.7, and opposite-signed pseudorapidities ηjet1 · ηjet2 < 0. The analysis is based on an inclusive dijet data sample collected by the CMS experiment in pp collisions during the low-luminosity run in 2015 at sqrt(s) = 13 TeV with an integrated luminosity of 0.66 pb−1 . The multiplicity of charged-particles with transverse momentum pT > 200 MeV in the fixed pseudorapidity interval |η| < 1 between the jets is used to define the central gap. The fraction of jet-gap-jet events, fCSE, is presented as a function of the pseudorapidity difference between the leading two jets, the transverse momentum of the subleading jet, and the azimuthal angle separation between the leading two jets. The results are compared to previous measurements by the D0, CDF, and CMS Collaborations and to perturbative quantum chromodynamics predictions based on the Balitsky-Fadin-Kuraev-Lipatov framework. The study also presents the first experimental observation of jet-gap-jet events with a leading proton, which yields the proton-gap-jet-gap-jet topology, using a subsample of events collected by the CMS and TOTEM experiments with an integrated luminosity of 0.4 pb-1. The leading protons are detected with the roman pot detectors of the TOTEM experiment. The ratio fCSE is found to be 2–4 times larger when a leading proton is included.
While the investigation of TMDs is a major objective of the EIC, Double Parton Ditributions (DPDs) are crucial for a first principle QCD description of double parton interactions at LHC, which contribute to the standard model background for various BSM searches. Both groups of functions are genuinely non-collinear and non-perturbative. The non-collinearity required the development of new concepts, most notably the introduction of soft factors. The soft factors for TMDs and DPDs turned out to be related. Lattice calculations are expected and actually needed to supplement the experimental efforts, e.g. at EIC and LHC but are significantly more difficult than for,e.g. PDFs. The talk will review the present status.
We consider the transverse spectrum and the $\cos 2\phi$ azimuthal distribution of $J/\psi$ mesons produced in semi-inclusive deep-inelastic electron-proton scattering, where the electron and the proton are unpolarized. At low transverse momentum, we propose factorized expressions in terms of transverse momentum dependent gluon distributions and shape functions. We show that our formulae correctly match with the collinear factorization results at high transverse momentum, obtained in the framework of collinear, nonrelativistic QCD. Moreover, we find that the perturbative tail of the shape function does not depend on the angular momentum of the charm-anticharm pair, initially produced in a color-octet state.
We present cross sections for the weak bosons measured by the STAR experiment at
RHIC in unpolarized proton-proton collisions at $\sqrt{s}$ = 500(510) GeV. The results combine data from run 2011, 2012, and 2013, corresponding to an integrated luminosity of 350~$pb^{-1}$. The differential $Z^{0}$ cross section measured as a function of the boson's $p_{T}$, provides important constraints on the energy dependence of intrinsic transverse momentum effects of partons inside the proton. The $W^{+}/W^{-}$ cross-section ratio as function of the boson's rapidity, is sensitive to the non-pertubative $\bar{d}/\bar{u}$ distribution. The probed $x$ range ($0.1 < x < 0.3$) covered by our data naturally complements the phase space accessed at the LHC, providing critical input to global fits.
We present an extraction of unpolarized transverse-momentum dependent (TMD) parton distribution functions (PDFs) based on a fit on data from Drell-Yan processes in different experiments and kinematic ranges, including in particular LHC experiments. The analysis is performed in the TMD factorization framework with perturbative accuracy up to next-to-next-to-next-to-leading-log (N$^3$LL), obtaining a remarkable agreement with data.
I present ongoing progress towards a new global PDF analysis from the NNPDF Collaboration: NNPDF4.0. As compared to its predecessor, NNPDF3.1, it contains several improvements from the theory input, dataset, and methodology points of view. NNPDF4.0 includes a large number of new experimental measurements from HERA, ATLAS, CMS, and LHCb, among others for the first time the HERA jet cross-sections, the ATLAS and CMS dijet distributions, and single top production. Theoretical calculations adopt NNLO QCD corrections in all cases and where relevant supplemented by NLO electroweak corrections including photon-induced contributions. A new fitting framework based on the TensorFlow machine learning tools has been developed, with an automated hyperparameter tuning carried out. We present preliminary results for NNPDF4.0 and compare it with NNPDF3.1 and other recent global PDF fits.
We present recent results from the xFitter project: an open-source
software framework for the determination of PDFs and the analysis of
QCD physics. xFitter has been used for a variety of LHC studies
including the measurement of the strange PDF, which we briefly
summarize. Additionally, charged current DIS charm production provides
a complementary perspective on s(x). We make use of the xFitter tools
to study the present s(x) constraints, and then use LHeC pseudo-data
to infer how these might improve. We also make use of the LHC
forward-backward asymmetry in neutral current Drell-Yan production to
help improve the up and down distributions. These studies provide
practical illustrations of the many features of xFitter.
A number of PDF sets have either recently been produced (CT18), or will be coming out in the near future (from MMHT, NNPDF), utilizing high statistics, high precision data from the LHC. In 2015, an intense year-long benchmarking exercise was carried out among the global PDFs then available (CT14, MMHT2014, NNPDF3.0). This exercise allowed a better understanding of the relative influence of the common data sets used in each PDF fit and the relationship between the PDF uncertainties calculated using the different techniques. This study allowed a combination of all three global PDFs in one common framework (PDF4LHC15). The PDF4LHC15 PDFs are now frequently used for theoretical precisions for the LHC. A new benchmarking exercise is now underway among the PDF sets containing precision LHC data that will lead to a future PDF4LHC20 set of PDFs. This talk will discuss the framework for the benchmarking and the available results.
The span of uncertainties of the PDFs obtained in a global analysis depends on criteria for selection of acceptable PDF fits. I review several such criteria for estimating the goodness of fit in a large-scale analysis such as CT18, where they are applied in addition to the commonly used value of the global log-likelihood. On the example of CT18(Z) predictions for electroweak precision observables, I show that these tests offer in-depth insights about agreement among constraints from individual experiments and other such factors that ultimately determine the realistic PDF uncertainty. I compare two particularly helpful statistical techniques for this purpose, Lagrange Multiplier scans and Hessian sensitivities.
The transverse momentum spectrum of low mass Drell-Yan (DY) production at low
center-of-mass energies $\sqrt{s}$ is calculated by applying transverse momentum
dependent (TMD) parton distributions obtained from the Parton Branching (PB)
evolution method, combined with the next-to-leading-order (NLO) calculation of
the hard process in the MCatNLO method. We compare our predictions with
experimental measurements at low DY mass, and find very good agreement. In addition
we use the low mass DY measurements at low $\sqrt{s}$ to determine the width $q_s$
of the intrinsic Gauss distribution of the PB-TMDs at low evolution scales. We find
values close to what has earlier been used in application of PB-TMDs to high-energy
processes at the Large Hadron Collider (LHC) and HERA. We find that low DY mass and
low $q_s$ even in the region of $p_t/m_{DY} \sim 1$ the contribution of multiple
soft gluon emissions (included in the PB-TMDs) is essential to describe the
measurements, while at larger masses and LHC energies the contribution from soft
gluons in the region of $p_t/m_{DY}\sim 1$ is small.
I will present the program “reSolve”, a publicly available tool for calculating the resummed contributions to transverse momentum and other spectra. It makes use of the Catani-de Florian- Grazzini resummation formalism in impact parameter space and Mellin space and exploits its largely process-independent nature to be general purpose, applying to any final state excluding coloured particles. So far reSolve has been used for diphoton, Drell-Yan and Z’ final states. I will discuss this briefly before presenting some ongoing work using reSolve, from the benchmarking of theoretical calculations of transverse momentum resummation for Drell-Yan to work examining searches for Z’s with large widths.
Precision physics calculation are now slowly becoming a standard in Monte Carlo event generation. In particular now, many MC generators allow the possibility to automatically include higher order EW-corrections on top of the usual QCD ones. Nevertheless these corrections can become quite computationally intensive, in particular for many-particles final states (or processes where one includes even higher order QCD corrections). EW-Sudakov logs represent the dominant contributions to the full NLO-EW corrections, and are based on ratio of tree-level amplitudes, and as such are much cheaper to compute than full EW-corrections. In this talk I will present a fully automated implementation of EW-Sudakov logs in the SHERPA MC generator. As well as showing comparisons with full EW-corrections, I will show a practical application in high-mass Drell-Yan computed at NNLO (QCD) + Sudakov EW matched to a parton shower.
The associated production of top quarks with neutral bosons is measurable in 13 TeV pp LHC collisions thanks to the unprecedented accumulated luminosity. It directly probes top quark couplings to photons and Z bosons and tests for deviations from the standard model.Three measurements are presented. The cross sections for the production of top quark pairs in association to a photon (ttgamma) or to a Z boson (ttZ) are measured both inclusively and differentially as a function of kinematic variables characterizing the tt+boson system. Both sets of measurements use the full Run2 data set consisting of 139/fb of integrated luminosity. Final states with three and four leptons and b-jets are used to extract ttZ rates, while ttgamma cross sections are derived from final states with one photon, one electron and one muon of opposite sign and at least two jets. The measurements are compared to predictions obtained by NLO+PS Monte Carlo and fixed order NLO calculations. Finally, 81/fb of integrated luminosity are used to search for flavour-changing neutral currents via the coupling of a top quark, a photon and an up or charm quark in events with one photon, one lepton (electron or muon), one b-tagged jet and missing transverse momentum.
We study the production of a single top quark in association with a heavy extra Z' at hadron colliders in new physics models with and without flavor-changing neutral-current(FCNC) couplings. We use QCD soft-gluon resummation and threshold expansions to calculate higher-order corrections for the total cross section and transverse-momentum distributions for tZ' production. The impact of the uncertainties due to the structure of the proton and scale dependence is also analyzed.
The talk will focus on physics goals with Run-III data and the status of ongoing and planned detector upgrades. A brief view on software upgrades and an outlook towards HL-LHC wiil also be presented.
Photoproduction at an electron-ion collider can be used to study many topics. Vector-meson photoproduction via photon-Pomeron interactions are a well-established method to study the gluon structure of nuclei. Reactions involving Reggeon exchange on proton targets can be used to study a wide variety of final state mesons, including charged mesons like the a_2^+ and Z_C^+ exotic; the photon-meson coupling is sensitive to the meson spin and structure. Backward photoproduction, where the vector meson recoils from the target nucleus, is also of interest at an EIC.
This talk will present some of the physics that can be studied at an EIC, with an emphasis on near-threshold reactions, photoproduction of exotica, and backward production, and then discuss the kinematics for different photoproduction reactions, with an emphasis on the detector requirements
The LHeC and the FCC-eh, offer unique prospects for the measurement of EW parameters and top properties in energy frontier, luminous ep scattering. In this talk we will revisit the determination of $Z$, $W$ and top mass through inclusive measurements. Next, we will show the possibilities for the determination of the vector and axial couplings of light quarks, of the effective weak mixing angle and of PDFs through electroweak interference probing the proton structure. We will discuss also direct W and Z production and the possibilities for determination of anomalous triple couplings. Finally, we will address top physics with the possibilities for precise determinations of the $Wtq$ couplings and competitive FCNC top coupling measurements.
Understanding the structure and dynamics of hadron structure entails the question how the roughly 1-GeV mass scale that characterizes the proton and atomic nuclei appears, and in stark contrast why are composite Goldstone bosons such as pions and kaons abnormally light in comparison. To understand this a strong interplay between experiment and theory is crucial. The talk will present the potential ground-breaking opportunities at the Electron-Ion Collider that, through the Sullivan process and proper tagging in the forward detector direction, can essentially present the possibility of electron-pion and electron-kaon scattering data of quality similar to the existing HERA electron-proton data, allowing detailed structure function maps, and also spatial and transverse momentum imaging data of the pion and kaon. A summary of the present status of the study will be presented including its impact on understanding of dynamical mass and requirements for the Electron-Ion Collider forward detector.
Pairing of nucleons at short-range is a universal phenomenon in nuclei, and has far-reaching implications outside of understanding traditional nuclear structure. Short-range correlations (SRCs) have been extensively studied over the past few years, using facilities around the world. Although this remarkable progress has brought deep, new insight into the nature of SRCs, there are still many unanswered questions. One of the most important and unresolved questions is how the EMC effect relates to these high-density, highly virtual nucleon states.
In my talk, I will present a broad overview of recent measurements of SRCs, focusing on our current work that illuminations the role of SRCs to the EMC effect. I will also discuss how we will further probe this connection in upcoming measurements and at future facilities, and how these future experiments will help use finally understand the EMC effect.
The dynamics among nucleons at short distances and the role QCD plays in it, is an outstanding problem in nuclear physics. It's understanding is important for uncovering the underlying physics of Short-Range Correlations (SRCs). In recent years, SRCs have been observed from light to heavy nuclei using fixed target experiments at Jefferson Lab via high energy electron-nucleus scattering. In this talk, I will talk about the opportunity of studying SRCs using light nuclei at the future Electron-Ion Collider (EIC). One experimental technique deployed is based on exclusive processes with tagging final-state particles, in order to fully control the initial state of the wave function. A few examples of physics cases will be briefly discussed. Recently, the spectral functions in light nuclei have been modeled within the BeAGLE event generator. In my talk I will discuss the decay kinematics of the light nuclei and their influence on the very forward detector design at the EIC .
I will present a new class of jet/event substructure observable called collinear drop and its use in the search for novel signatures of jet modifications and medium responses. I will demonstrate using Monte Carlo simulations generated with Jewel how underlying jet-medium interactions can be systematically examined using collinear-drop observables. I will also give analytic insights on the modifications of such observables using soft-collinear effective theory with Glauber gluon interactions. Studies using LEP open data and applications to DIS will be presented.
Measurements of the internal properties of jets allow QCD to be studied at a new regime at a hadron collider. In this talk, we discuss recent measurements of jet substructure and jet fragmentation that were performed using data collected by the ATLAS experiment at a centre-of-mass energy of √s=13 TeV. For jet substructure, a comprehensive suite of substructure observables are measured for jets reconstructed with the soft-drop algorithm applied. In addition, a measurement of the Lund Plane is performed using charged particles. The fragmentation properties of jets, such as the jet charge and summed fragmentation function, are also measured using charged particles. Finally, if ready, a measurement of the fragmentation properties of jets containing B-hadrons will also be presented. All of the measurements are corrected for detector effects and are compared to the predictions of state-of-the-art Monte Carlo event generators.
We study the angle between i) the standard jet axis, ii) the axis of a jet
which has been groomed using soft drop, with reduced sensitivity to soft radiation, iii) the
jet axis obtained with the winner-take-all recombination scheme, which is insensitive to
soft radiation at leading power. We calculate the distributions for these angles at next-to-leading logarithmic accuracy, including non-global logarithms. The angle between the
standard and groomed jet axis directly probes soft wide-angle radiation, leading to a novel
factorization formula. This angle is also very sensitive to nonperturbative physics, which is
directly connected to nonperturbative contribution to the rapidity anomalous dimension for
transverse momentum distributions. Comparing our predictions to Pythia we find good
agreement, and we foresee applications to jet substructure in proton-proton and heavy ion collisions. In addition, the new observables are ideally suited for low energy jets at the future Electron-Ion Collider as hadronization corrections are well understood.
Jet substructure represents a cornerstone in current BSM searches at the LHC. Further, it is instrumental in the on-going endeavor to pinpoint the effect of a hot, thermal medium, namely the QGP, on QCD dynamics. In this talk, based on [1], I will present a new set of jet substructure observables and an associated grooming technique rooted on identifying the hardest splitting in an angular ordered shower and discarding prior splittings that occur at larger angles. First, I will use p+p collisions to benchmark the method with pQCD calculations through the computation of the Sudakov form factor at modified leading-log accuracy in the context of vetoed showers. I will compare the analytic properties of the dynamically tagged splitting such as its momentum sharing fraction with Monte Carlo simulations. In addition, the resilience of the method to non-perturbative effects together with its performance on quark/gluon discrimination and boosted W/t/H tagging will be assessed.
[1] arXiv:1911.00375
Studies on the production of light- and heavy-flavour baryons are of prominent importance to characterise the partonic phase created in ultrarelativistic heavy-ion collisions and to investigate hadronization mechanisms at the LHC, in particular through the study of the evolution of the baryon-over-meson production ratio as a function of the transverse momentum. Measurements performed in pp and p-Pb collisions at the LHC, have revealed unexpected features, qualitatively similar to what observed in larger systems and, in the charm sector, not in line with the expectations based on previous measurements from e+e- colliders and from DIS measurements in e-p collisions at HERA.
These results suggest that charmed baryon formation might not be universal and that the baryon-over-meson ratio depends on the collision system. Hints of non-universality of the fragmentation functions are also seen when comparing beauty-baryon production measurements at the Tevatron and LHC with those at LEP. Models that better reproduce the $\Lambda_c$/$D^0$ ratio in pp collisions, some of them based on enhanced color reconnection mechanisms, expect a significant contribution to $\Lambda_c$ yield from decays of heavier charm-baryon states.
The ALICE detector is well suited to detect charm baryons down to low $p_{\rm T}$ thanks to the excellent tracking capabilities and state-of-art particle identification. In pp and Pb-Pb collisions, $\Lambda_c$ baryons are reconstructed in the hadronic decay channels $\Lambda_c\rightarrow pK^0_s$ and $\Lambda_c\rightarrow pK\pi$ by means of machine-learning methods.
A review of ALICE extensive measurements of protons, hyperons and charmed baryons, including, in the pp system, the measurement of $\Lambda_c$ production as a function of charged-particle multiplicity, will be presented. Comparison to phenomenological models and to previous measurements at DIS experiments will be also discussed. Emphasis will be given to the discussion of the impact of these studies on our understanding of hadronization processes. Finally, the status and prospects for $\Xi_c$ and $\Sigma_c$ measurements, as well as, the planned measurements of $\Lambda_b$ during LHC RUN3 data taking will be also discussed.
The LHCb experiment at the Large Hadron Collider (LHC) at CERN is suited for studying various aspects of the theory of strong interaction, Quantum Chromo-Dynamics. One area of active research is to understand how hadrons are formed from scattered quarks and gluons, collectively referred to as partons, in energetic proton-proton collisions. The hadronization process is a non-perturbative phenomenon unlike hard scattering of partons and their shower processes, and thus can only learned from data such as jet substructure measurements. Equipped with a forward spectrometer covering pseudo-rapidity of 2:0 < eta < 5:0, the LHCb experiment achieves a transverse momentum resolution of Delta pT/ pT <1% up to 200 GeV /c for charged tracks and a jet pT resolution of <15%. This along with excellent particle identification capabilities offer a unique opportunity to measure with great precision hadronization variables defined to characterize multi-dimensional hadronization processes and their flavor dependence within jets. Recently published results for measurements of nonidentified hadrons within light quark-initiated jets analyzed Run-I data with an integrated luminosity of 2 fb-1 taken in p+p collisions at center-of-mass energy sqrt(s) = 8 TeV. A larger dataset is available for sqrt(s) = 13 TeV from Run-II data that enables measurements of identified hadrons for the first time.In addition, hadronization measurements within heavy flavor tagged jets are under way. This talk will present the published results as well as the status of ongoing measurements.
The central issue of the presentation will be theoretical study of four charged pion photoproduction that come from ultraperipheral heavy-ion collision. I take into account the single photoproduction of the radial excitations of the $\rho^0$ vector meson. The analysis includes a contribution from the incoherent sum of the $\rho'(1450)$ and $\rho''(1700)$ vs single $\rho(1570)$ vector mesons. I will show that my theoretical model has very good agreement with the experimental data for PbPb $\to$ PbPb$\pi^+\pi^-$ mechanism. The proposed phenomenology works for the photoproduction of vector meson that decays into a two-pion channel thus using a new H1 experiment data for $\gamma p \to 2\pi^+2\pi^-$ process one can make predictions for four charged pions productions in ultra-peripheral heavy ion collisions. I will present the differential and total cross section for the PbPb $\to$ PbPb2$\pi^+$2$\pi^-$ process. Finally, I have got even one order of magnitude larger (at midrapidity) cross section than it was predicted using STARlight generator. Obtained results constitute a comprehensive analysis of $\rho^0(770)$ meson excited states that decay into $2\pi^+2\pi^-$ channel.
The electromagnetic field of a fast charged particle can be described as a flux of quasi-real photons whose intensity is proportional to the square of the electric charge of the particle. In the case of lead ions circulating in the LHC there are copious photonuclear interactions. If the impact parameter of the colliding lead ions is larger than the sum of their radii, photon-induced processes dominate the interaction rate via ultra-peripheral collisions (UPC). The study of a \rho^0 meson photonuclear production is important, because its cross section in Pb–Pb UPC at the LHC is so large that it becomes a proper tool to research the approach to the black-disk limit of QCD.
First measurements of the cross sections for the coherent photoproduction of \rho^0 mesons in Pb--Pb UPC at sqrt(s_NN)=5.02 TeV with the ALICE experiment at LHC are presented in three regions of rapidity covering the range |y|<0.8. At each rapidity, cross sections are given for different nuclear-breakup classes defined according to the presence of neutrons measured in zero-degree calorimeters.The results are compared with those from lower energies and with model predictions.
The method used to extract the different contributions for the photonuclear processes to the UPC cross section has been improved using forward neutron classes, which is specially important in view of the expected data samples to be recorded at the LHC during the Run 3 and 4.
Finally, the observation of a coherently produced resonance-like structure with a mass around 1.7 GeV/c^2 and a width of about 140 MeV/c^2 is reported and compared
with similar observations from other experiments.
In recent years the STAR Collaboration collected a large sample
of ultra-peripheral heavy-ion collisions. The photoproduction of
J/Psi vector mesons is sensitive to the gluon content of the target
nucleon or nucleus. We will present results from a statistically
large sample of J/Psi production in Au+Au collisions. A significant
result comes from the study of the pT distributions, which clearly
show two components, from scattering off the entire Au nucleus or off
individual nucleons inside the nucleus. From a smaller sample of J/Psi
production in p+Au collisions, with polarized protons, we will discuss
the status of a first study of the asymmetry of J/Psi production.
A non-zero asymmetry would be the first measure of the generalized
parton distribution, E, for gluons, which is connected with the
orbital angular momentum of partons in the nucleon. The present study
is a proof-of-principle, and we will discuss the possibilities with
larger data samples from future polarized p+p and p+Au RHIC runs.
The high flux of quasi-real photons from fast moving lead ions at the LHC allows us to study photon-induced reactions in ultra-peripheral collisions (UPC) of Pb-Pb nuclei in a new kinematic regime. In addition, this flux makes it possible to study J/$\Psi$ exclusive photoproduction off protons in p-Pb collisions at the LHC. Measuring the scattering angle of the produced vector meson one can compute the centre-of-mass energy of the photon-proton or photon-Pb scattering. This allows us to use these collisions to study the energy evolution of the gluon content of the target.
The newest ALICE results on vector meson photoproduction in UPC Pb-Pb in the forward and central rapidity region, and p-Pb collisions from LHC Run 2 are presented. These results provide new stringent tests for models of saturation and shadowing at small-x. The measurements are compared to the newest models of this process. In addition, prospects for heavy vector meson photoproduction measurements in LHC Run 3 and 4 will be presented.
We investigate saturation e?ffects in ep scattering as well as in ultraperipheral pA and AA collisions at small x with four variants of the impact parameter dependent color dipole model: with and without gluon saturation and with and without a novel mechanism that suppresses unphysical dipole radii above the confinement scale.
We show that ep scattering at HERA can be very well described by any of
the four variants. When going from ep to eA scattering, saturation effects are expected to increase with increasing A. In lieu of an electron-ion collider (EIC), we confront the different versions of the dipole model with data recorded in ultraperipheral collisions at the LHC in order to estimate the sensitivity of the data to gluon saturation in the target nuclei. We also report on new prediction for the EIC.
We present a model with which we predict the cross sections for exclusive and dissociative photo and electroproduction of light and heavy vector mesons off protons; the model describes correctly available experimental data. The model is based on the color-dipole approach and incorporates geometric fluctuations of the target-proton partonic structure in the impact-parameter plane. The number of fluctuations grows with decreasing Bjorken-x and they are generated as event-by-event randomly placed areas of high gluonic density, so-called hot spots. A striking feature of the model is the prediction of a maximum of the dissociative cross section as a function of the center-of-mass energy $W_{\gamma p}$, followed by a steep decrease as the hot spots start to overlap with increasing energy. We use these maxima to define a geometric saturation scale which grows linearly with energy as a function of the scale of the process. This phenomenon can be measured at the proposed electron-ion colliders such as eRHIC or LHeC. We present a comparison of their envisioned kinematic reach with the geometric saturation scale.
We show how exclusive vector meson production off light ions can be used to probe the spatial distribution of small-𝑥 gluons in the deuteron and 3He wave functions. In particular, we demonstrate how short range repulsive nucleon-nucleon interactions affect the predicted coherent J/Psi production spectra. Fluctuations of the nucleon substructure are shown to have a significant effect on the incoherent cross section above |t|>0.2 GeV^2. By explicitly performing the JIMWLK evolution, we predict the x-dependence of coherent and incoherent cross sections in the EIC energy range. Besides the increase of the average size of the nucleus with decreasing x, both the growth of the nucleons and subnucleonic hot spots are visible in the cross sections. The decreasing length scale of color charge fluctuations with decreasing 𝑥 is also present, but may not be observable for |t|<1 GeV^2, if subnucleonic spatial fluctuations are present.
References
H. Mäntysaari, B. Schenke, e-Print: arXiv:1910.03297, accepted for publication in Phys. Rev. C
I will discuss complications that arise in the factorization of hard processes differential in transverse momentum due to ambiguities in the transition from the small to large transverse momentum regions. I will relate questions about the region transition to the implementation of evolution in transverse momentum sensitive processes such as spin asymmetries. In addition, I will relate the discussion to the implementation of evolution in recent phenomenological studies.
COMPASS is a fixed target experiment in operation at CERN since 2002, with
a research program focused on the structure of the hadrons and spectroscopy.
An important part of this program is the study of transverse spin and momentum
dependent parton distribution and fragmentation functions. A review of recent
results on TMDs obtained by using muon beams scattering off unpolarised and
polarized targets will be given. The perspectives for the 2021 approved run
when using a transversely polarized deuteron target will also be discussed.
I will discuss the cross section for the production of two unpolarized hadrons in the large transverse momentum configuration from $e^+ e^-$ annihilation, which is based on collinear fragmentation functions (FFs). Comparing with standard transverse-momentum-dependent (TMD) FF-based predictions intended for the small transverse momentum region, when the center of mass energy is not very large we find significant tension in the intermediate transverse momentum region, where the collinear factorization-based and TMD factorization-based calculations should instead roughly coincide. Measurements based on $e^+ e^-$ annihilation are ideal to explore the large-to-small transverse momentum transition, given the typically larger hard scales (>10 GeV) of the process, as compared with similar scenarios that arise in semi-inclusive deep inelastic scattering and fixed-target Drell-Yan measurements.
A complete understanding of the nucleon spin structure requires the knowledge of unpolarized parton distribution functions, helicity distribution functions, and the transversity distributions. Transversity, which describes the transverse spin structure of quarks in a transversely polarized proton, is the most difficult to probe and is still quite unconstrained in global analyses. It is chiral-odd and can only be accessed through channels that couple to another chiral-odd distribution like the Collins fragmentation function or the interference fragmentation function. Recently, STAR reported the first measurements of Collins asymmetries from jet + $\pi^{\pm}$ production in polarized proton+proton collisions at $\sqrt{s}$ = 500 GeV and 200 GeV based on the data taken during the years 2011 and 2012. These results probe higher momentum scales ($Q^{2}$ $\sim$ 960 $\mathrm{GeV^{2}}$ for 500 GeV and $\sim$ 170 $\mathrm{GeV^{2}}$ for 200 GeV) than the measurements from semi-inclusive deep inelastic scattering (SIDIS, $Q^{2}$ $<$ 20 $\mathrm{GeV^{2}}$) and enable the test of the evolution, universality and factorization breaking in the transverse momentum dependent (TMD) formalisms. New preliminary results for the Collins asymmetry from 2015 proton+proton collisions at $\sqrt{s}$ = 200 GeV with a much larger sample size and improved analysis procedures that lead to smaller systematic uncertainties will be presented.
We present recent results of transverse single spin asymmetries (TSSAs) for neutral pions using the Forward Meson Spectrometer at STAR at center of mass energies of 200 and 500 GeV in proton-proton collisions. Combining the results from the two energies shows that the pion TSSA increases monotonically with Feynman-x. Comparisons with previous measurements show that the pion TSSA is mostly independent of the center of mass energy from 20 GeV to 500 GeV. It is found that pions with no nearby particles tend to have a larger TSSA than isolated pions, which may suggest different mechanisms for the TSSAs for different sub-groups of pions. In order to separate the contributions from initial and final state effects at both energies, we have also measured TSSAs for the electromagnetic jets and the Collins asymmetry through the TSSA of neutral pions inside the electromagnetic jets. The jet TSSA follows the Feynman-x behavior of the pion TSSA, but with a significantly smaller amplitude. The Collins asymmetry is consistently small across all the studied $z_{em}$ and $j_{T}$ bins, which refers to the neutral pion energy fraction and the neutral pion transverse momentum projection onto the jet axis, respectively. These results provide rich information to understand the neutral pion TSSA.
We present a new extraction of unidentified charged hadron collinear fragmentation functions (ffs) using a multi-step Monte Carlo analysis. The extraction utilizes available charged hadron data from e+/e- and SIDIS experiments including the most recent results from COMPASS.
The lack of a neutron target has resulted in a decades-long effort to understand the free neutron structure in order to test SU(6) symmetry breaking mechanisms. Approaches to address this open question traditionally extract the free neutron structure from proton + deuterium DIS data (and various other reactions such as jet production or W charge asymmetries).
Here we present a novel approach to extracting the free neutron structure by utilizing all available structure functions of nuclei (from deuterium to lead), while consistently accounting for partonic medium-modifications in atomic nuclei. Using such a wide span of nuclei provides a large lever arm that allows us to precisely constrain the neutron structure function, even at high-x.
We also discuss extracting the free neutron structure from A=3 nuclei, as proposed by the MARATHON collaboration, and the theoretical uncertainties associated with such an extraction. We present a complimentary approach to extracting the free neutron structure from A=3 nuclei with a convolution model.
In the global analysis of nuclear Parton Distribution Functions
(nPDFs), one of the major sources of debate is how to include the
neutrino Deep Inelastic Scattering (DIS) data. The controversy comes
from the precise NuTeV neutrino DIS data which might indicate an
incompatibility with neutral current charged lepton DIS data. The
compatibility of NuTeV data was studied independently by several
PDF-fitting groups, and the results are without consensus. In this
work, we re-examine the neutrino DIS data with special emphasis on the
normalization error in the NuTeV data. Precise understanding of the
neutrino DIS will help determine the strange content of the proton.
We report on our progress of including the latest LHC p-Pb measurements on W$^\pm$, dijet, and D-meson production into the EPPS analysis of nuclear PDFs. The new data are observed to set strong constraints particularly on the gluons across a wide range in the momentum fraction $x$.
What new tools will we need for determining nuclear PDFs
at the HL-LHC, LHeC, and EIC in the next decade?
Current W/Z data from LHC is challenging our preconceptions
of the strange PDF. New hi-x data at low-Q from JLab push us
into the region of higher-twist and non-perturbative effects.
We provide an update of some nCTEQ progress in these areas,
and look ahead to characterize the impact of the future facilities
on our precision QCD measurements.
The nCTEQ15 fit of nuclear Parton Distribution Functions (nPDFs)
includes data on Deep Inelastic Scattering (DIS), Drell-Yan (DY) and
single-inclusive pion production. In preparation for the upcoming
nCTEQ nPDF update, we present an analysis assessing the impact of
additional single-inclusive hadron production data in a nCTEQ15-like
fit. Specifically we look at pion production data from all RHIC and
LHC experiments. Furthermore, we investigate the resulting dependence
on the fragmentation functions.
Resolving the quark and gluon structure of nuclei has been a crucial aim of the QCD physics community since the discovery of the EMC effect. Such information is given by the nuclear parton distribution functions (nPDFs), which describe the collinear momentum substructure of nucleons bound within nuclei and are accessed via global QCD analyses of lepton-nucleus and hadron-nucleus measurements. In this talk, I present an updated global QCD analysis of nPDFs based on the NNPDF methodology. This analysis follows a previous study which implemented for the first time both a model-independent atomic mass dependence of the PDFs using neural networks, and a Monte Carlo technique for estimating PDF uncertainties. In particular, I will highlight the impact of vector boson and dijet production measurements from pPb collisions at the LHC as well as discuss potential constraints from the LHC and future DIS colliders such as the EIC and LHeC.
In preparation for the era of the High-Luminosity LHC, it will be crucial to enhance the precision of theoretical predictions for BSM-sensitive observables in the electroweak and Higgs sectors. In many cases, such as the extraction of the $W$-boson mass, contemporary PDF uncertainties are a dominant limitation in the quest to achieve the necessary precision. In this talk, I will review this problem and deploy several novel analysis techniques to parse PDF uncertainties relevant for electroweak precision observables at the LHC. I will also highlight the important role to be played by next-generation measurements from DIS colliders like the Electron-Ion Collider (EIC).
Possible electroweak and beyond the Standard Model searches at the future Electron-Ion Collider will be discussed. Measurements of the charged current reactions, parity violating asymmetries, as well as possible searches for e-tau charged lepton flavor violation will be reviewed. This talk will discuss importance of the beam polarization, high luminosity and benefits of the positron beam.
In ultra-relativistic heavy-ion collisions, one expects copious rates of γγ processes through the interaction of the large electromagnetic fields of the nuclei, which can produce new particles (e.g. leptons) or even lead to light-by-light scattering via loop diagrams. The latter process is a notable prediction of QED and was only recently observed by ATLAS using the full 2018 dataset. In ultra-peripheral collisions (UPCs), characterized by large impact parameter between the nuclei, the outgoing leptons and photons are produced exclusively, and exhibit a strong back-to-back momentum correlation, with long tails induced by higher-order QED effects. This talk presents measurements of dilepton production and light-by-light scattering performed by the ATLAS collaboration. The angular correlations as well as differential production cross sections in UPCs are measured and compared to theoretical models, including final state QED radiation. The role of forward neutron production in disentangling pure QED and dissociative processes will also be discussed. Finally, limits on axion-like particle production, from the observed light-by-light cross sections, will be discussed. Muon pairs produced the same two-photon scattering process in hadronic Pb+Pb collisions also potentially provide a sensitive probe of the quark gluon plasma. First measurements by ATLAS and STAR of dileptons produced via two-photon scattering in non-ultra-peripheral (non-UPC) nucleus-nucleus collisions showed an unexpected centrality-dependent broadening of the angular correlation between the two leptons and/or of the two-lepton pT distribution. ATLAS has recently measured dimuons produced via two-photon scattering in non-UPC Pb+Pb collisions at √sNN= 5.02 TeV using data collected during the 2018 Pb+Pb run at the LHC corresponding to an integrated luminosity of 1.73/nb. This data set represents a factor of ~4 increase in statistics over the 2015 data set used for the first ATLAS measurement. The increased statistics allow new features to be observed in the data, as well as differential studies of the dependence of the pair-distribution on the transverse-momentum and pseudorapidity of the two muons. The results of the new measurement and the possible physics implications will be discussed.
Latest results from the NA62 experiment at CERN.
The NA62 experiment at the CERN SPS is designed to measure the branching ratio of the K+→π+vv ̅ decay, one of the best candidates to reveal indirect effects of new physics at the highest mass scales with a very precisely predicted branching ratio of less than 10-10.
NA62 took data in 2016-2018.
Data statistics collected in 2016 allowed NA62 to reach the Standard Model sensitivity for K+→π+vv ̅, entering the domain of 10-10 single event sensitivity and showing the proof of principle of the experiment. Thanks to the statistics collected in 2017, NA62 surpasses the present best sensitivity. The analysis strategy is reviewed and the preliminary result from the 2017 data set is presented.
The sensitivity to a range of lepton flavour and lepton number violating kaon decays provided by the NA62 data set improves over the previously reported measurements. Results from the searches for these processes with a partial NA62 data sample are presented.
A high-intensity fixed-target setup and detector performance make the NA62 experiment particularly suited for searches of new physics from faintly interacting particles in the MeV—GeV mass range: heavy-neutral leptons, axion-like particles, and others. The results from the analysis of data taken with dedicated setup and triggers developed to this purpose will be highlighted.
The STAR Collaboration designs, constructs, and installs a suite of new detectors in the forward rapidity region (2.5 < eta < 4) over the next two years, enabling a program of novel measurements in pp, pA, and AA collisions. This extension of STAR’s kinematic reach will allow detailed studies of cold QCD physics at both very high and very low partonic momentum fraction, i.e. when the colliding quarks and gluons carry very large or very small amounts of the nucleon energy. Previous STAR efforts using the Forward Pion Detector (FPD) and Forward Meson Spectrometer (FMS) detectors have demonstrated that there are outstanding QCD physics opportunities in the forward rapidity region. To fully explore these physics opportunities, the forward upgrade [1] has detection capability for neutral pions, hadrons, photons, electrons, and jets, and adds charged-particle tracking, electromagnetic, and hadronic calorimetry to STAR’s capabilities at high pseudorapidity. The upgrade will greatly expand the kinematic reach for ongoing measurements of the spin and flavor structure of the nucleon, and will enable studies of the longitudinal structure of the nuclear initial state that leads to breaking of boost invariance in heavy-ion collisions. Transport properties of the hot and dense matter formed in heavy-ion collisions will also become accessible with the new measurement capabilities at forward rapidity. Details on the planed upgrade and the scientific opportunities it will enable will be presented.
[1] “The STAR Forward Calorimeter System and Forward Tracking System,” https://drupal.star.bnl.gov/STAR/starnotes/public/sn0648
The design of the future electron-ion collider EIC at Brookhaven National
Laboratory has been continuously evolving towards a realistic, low-risk design
that meets all the requirements set forth by the nuclear physics community in
the White Paper. Over the past year activities have been focused on maturing the
design, and on developing alternatives to mitigate risk. These include
modifications to the interaction region, converting the second RHIC ring into
a full-energy hadron injector, and modifications of the hadron ring vacuum
system to accommodate the high average and peak beam currents.
We will present the eRHIC design with a focus on recent developments.
We present an overview of the Interaction Region (IR) design for the Electron Ion Collider (EIC), which will be located at Brookhaven National Laboratory (BNL). The IR is designed to meet the requirements of the nuclear physics community as outlined in [1].
The IR design features a +/-4.5 m free space for the detector; a forward spectrometer magnet is used for the detection of hadrons scattered under small angles. The hadrons are separated from the neutrons allowing to detect neutrons up to +/-4mrad. On the rear side the electrons are separated from photons using a weak dipole magnet for the luminosity detector and to detect scattered electrons (e-tagger).
In this paper we will show the present status of the design and discuss some of the design challenges.
[1] An Assessment of U.S.-Based Electron-Ion Collider Science. (2018). Washington, D.C.: National Academies Press. https://doi.org/10.17226/25171
Measurements at the EIC have stringent requirements on high luminosity and acceptance of the collision final state particles, particularly in the directions along the beamline or, equivalently, extremely high rapidity. Accessing the EIC physics of interest requires unprecedented integration of the interaction region and detector designs. In this presentation, we review current detector concepts of the EIC, in particular a total acceptance detector is that achieves close to full acceptance for the scattered electron and the particles associated with the initial state ion and struck quark, respectively. We also show selected highlights from the ongoing Yellow Report studies for the EIC.
We present a theoretical formalism and associated results for soft-gluon resummation for $2 \rightarrow n$ processes in single-particle-inclusive kinematics.
The factorization of short-distance partonic cross sections from universal nonperturbatively-generated kinematic distributions is fundamental to phenomenology at hadron colliders. It has been predicted however that certain observables cannot be factorized in the usual way, even at high energies. Specifically, observables that are sensitive to momenta transverse to the direction of an energetic parton or hadron cannot be factorized with the standard basis of nonperturbative functions, instead requiring a larger basis of functions with significantly less universality. It should be possible to probe the effects of factorization breaking using Z+jet production in high-energy proton-proton collisions by studying azimuthal correlations between a Z boson and unidentified charged hadrons. This talk will introduce a plan to perform this measurement with data collected by LHCb at a center of mass energy of 13 TeV. Related work will also be discussed.
The status of the three-loop heavy-flavor corrections to unpolarized and polarized deep-inelastic scattering is reviewed. We discuss the analytic results on the single and two-mass corrections and also outline the consequences for the variable flavor number scheme in high energy hadronic scattering and heavy quark distribution functions.
Abstract In this talk we present our theoretical results for the multiplicity dependence of $J/\psi$ production and compare it with recent experimental data from STAR and ALICE collaborations. We argue that a rapidly growing multiplicity dependence presents a strong evidence in favor of multigluon fusion mechanisms of the quarkonia states. We demonstrate that the experimentally observed multiplicty dependence might be described by 3-gluon fusion mechanism, whereas conventional 2-gluon fusion mechanism underestimates the experimental data. We also show that the 3-gluon fusion can correctly describe the shape of the rapidity and transverse momentum dependence, and potentially could give a sizeable contribution to produced quarkonia yields. We also make predictions for other $1S$-quarkonia states, such as $\psi(2S)$ and $\Upsilon(1S)$, and demonstrate that the multiplicity dependence for these states should be close to multiplicity dependence for $J/\psi$.
This presentation is partially based on our recent submission https://arxiv.org/abs/1910.13579.
We study exclusive quarkonium production in the dipole picture at next-to-leading order (NLO) accuracy, using the non-relativistic expansion for the quarkonium wavefunction. This process offers one of the best ways to obtain information about gluon distributions at small $x$, in ultraperipheral heavy ion collisions and in deep inelastic scattering. The quarkonium light cone wave functions needed in the dipole picture have typically been available only at tree level, either in phenomenological models or in the nonrelativistic limit. In this talk, we discuss the compatibility of the dipole approach and the non-relativistic expansion and compute NLO relativistic corrections to the quarkonium light-cone wave function in light-cone gauge. Using these corrections we recover results for the NLO decay width of quarkonium to $e^{+}e^{-}$ and we check that the non-relativistic expansion is consistent with ERBL evolution and with B-JIMWLK evolution of the target. The results presented here will allow computing the exclusive quarkonium production rate at NLO once the one loop photon wave function with massive quarks, currently under investigation, is known. This talk is based on ArXiv:1911.01136
We start with an overview of the recent results on charmonia and bottomonia production in electro- and photoproduction processes. An emphasis will be given to the careful treatment of light-front wavefunctions of heavy quarkonia in the potential approach formulated in the color dipole picture. A significant role of spin effects and the D-wave component is found and quantified. Our light-front approach is then applied to the analysis of both the ground-state and excited quarkonia photoproduction observables in ultra peripheral proton-nucleus and nucleus-nucleus collisions and the results are confronted with the recent data from the LHC. Finally, we report on the first results on quarkonia hadroproduction in the light-front potential approach.
Fully instrumented in the forward acceptance, LHCb provides the unique capabilities to study nuclear environment using open and hidden heavy flavor production in the forward region. In this talk, we present the recent LHCb measurements of open charm hadron production in pPb collisions at sqrt(s_NN)=8.16 TeV, event-activity dependent chic1(3872) production in pp collisions at sqrt(s)=8TeV, and coherent Jpsi production in ultra-peripheral PbPb collisions at sqrt(s_NN)=5 TeV. The open charm production is measured down to zero pT, which strongly constrains the nuclear parton densities at low Bjorken-x~10^-5, where parton saturation may happen. UPC Jpsi produced from the interaction of a dense electromagnetic field with the Pb nucleus allows to study the nuclear PDF in a clean environment. Measurement of chic1(3872) production in correlation with the event activity helps to understand its internal structure and bound state dissociation through interaction with collision final states. LHCb results in fixed-target collisions and prospects for Run3 are also presented.
We report on the measurement of the Central Exclusive
Production of charged particle pairs $h^{+}h^{-}$ ($h = \pi, K, p$)
with the STAR detector at RHIC in proton-proton collisions at
$\sqrt{s} = 200$ GeV. The charged particle pairs produced in the
reaction $p+p \rightarrow p^\prime+h^{+}h^{-}+p^\prime$ are reconstructed from
the tracks in the central detector and identified using the specific
energy loss and the time of flight method, while the forward
scattered protons are measured by the Roman Pot detectors.
Exclusivity of the event is guaranteed by requiring transverse
momentum balance of all four final state particles. Differential
cross sections are measured as functions of observables related to
the hadronic final state and to the forward scattered protons. They
are measured in a fiducial region corresponding to the acceptance of
the STAR detector and determined by the central particles'
transverse momentum and pseudorapidity as well as by the forward
scattered protons mome
nta. This fiducial region roughly corresponds to the square of the
four-momenta transfers at the proton vertices in the range $0.04 <
-t_1 , -t_2 < 0.2$ GeV$^2$ and invariant masses of the charged
particle pairs up to a few GeV.
The measured cross sections are compared to phenomenological
predictions based on the Double Pomeron Exchange (DPE) model.
Structures observed in the mass spectra of $\pi^{+}\pi^{-}$ and
$K^{+}K^{-}$ pairs are consistent with DPE model while angular
distributions of pions suggest dominant spin-0 contribution to
$\pi^{+}\pi^{-}$ production. For $\pi^+\pi^-$ production fiducial cross
section is extrapolated to Lorentz invariant region which allows
decomposition of the invariant mass spectrum into continuum and
resonant contributions. Extrapolated cross section is well described
by the continuum production and at least three resonances,
$f_0(980)$, $f_2(1270)$ and $f_0(1500)$, with a possible small
contribution of $f_0(1370)$. Fits to extrapolated differential cross
section as a function of $t_1$ and $t_2$ enabled the extraction of
the exponential slope parameters in several bins of invariant masses
of $\pi^+\pi^-$ pairs.
Central exclusive production at hadron colliders results in a hadronic state at or close to midrapidity, and forward scattered protons. The rapidity range between the midrapidity tracks and the forward scattered system is void of particles, thereby yielding a double gap topology which can be identified experimentally. At the high energies of the LHC, pomeron-pomeron fusion dominates the central exclusive production process in proton-proton collisions. I will summarise the approaches to model such reactions, and will discuss the ongoing efforts in the ALICE collaboration to analyse double gap events taken in Run II at the LHC, with particular emphasis on the strangeness sector. The prospects of such data taking in Run III will be presented.
The analysis of single transverse-spin asymmetries (SSAs) gives us tremendous insight into the internal structure of hadrons. For example, the Sivers and Collins effects in semi-inclusive deep-inelastic scattering (SIDIS), Sivers effect in Drell-Yan, and the Collins effect in electron-positron annihilation have been widely investigated over many years in order to perform 3D momentum-space tomography. In addition, observables like $A_N$ in proton-proton collisions are of interest due to their sensitivity to quark-gluon correlations. In this talk I will report on the first global fit of SSA data from SIDIS, Drell-Yan, $e^+e^−$ annihilation into hadron pairs, and proton-proton collisions. I will discuss the results of our analysis, including the extraction of a unique set of universal non-perturbative functions that describe all observed SSAs, and also explore avenues for future research.
Transverse spin phenomena have challenged our understanding of the structure of the nucleon and the strong interaction in many ways. The single transverse spin asymmetries that were measured at RHIC continue to challenge us as the contributions from initial and final state effects as well as the contributions from various flavors are not well understood. The PHENIX experiment has contributed various newer measurements of charged muons and hadrons at forward rapidities as well as neutral mesons at central rapidities. These measurements as well as the status of direct photon asymmetries at sqrt{s}= 200 GeV at central rapidities, which are sensitive essentially only to initial-state effects, will be presented.
We perform a systematic study on the twist-3 gluon distribution and fragmentation
functions which appear in the collinear twist-3 factorization for hard inclusive
processes. Three types of twist-3 distribution and fragmentation functions,
i.e., intrinsic, kinematical and dynamical ones, which are necessary to describe
all kinds of twist-3 cross sections, are related to each other by the operator
identities based on the QCD equation of motion and the Lorentz invariance
properties of the correlation functions. We derive the exact relations for all
twist-3 gluonic distribution and fragmentation functions for a spin-1/2 hadron.
Those relations allow one to express intrinsic and kinematical twist-3 gluon
functions in terms of the twist-2 and dynamical twist-3 functions, which provides
a basis for the renormalization of intrinsic and kinematical twist-3 functions.
In addition, those model independent relations are crucial to guarantee gauge
invariance and frame independence properties of the twist-3 cross sections.
Through the 21st and 22nd International Workshop on Deep Inelastic Scattering, a possibility of the non-perturbative contribution for the non-zero transverse single spin asymmetry of forward $\pi^{0}$ ($2 < \eta < 4$) was brought up. Bigger asymmetry was observed with more isolated final state which was connected with the non-perturbative event topology. Since the non-perturbative contribution has been studied by only the forward $\pi^{0}$ production where the perturbative process was expected to be the major interaction rather than non-perturbative one, the RHICf experiment measured the very forward ($\eta > 6$) $\pi^{0}$ to study the non-perturbative contribution in more detail. A new electromagnetic calorimeter was installed for the operation at the zero-degree region of the STAR experiment at RHIC and measured the $\pi^{0}$ over the kinematic range of $x_{F} > 0.25$ and $0 < p_{T} < 1$ GeV/$c$ in June, 2017. A clear non-zero asymmetry was observed even in low $p_{T} < 1$ GeV/$c$ showing a similar $x_{F}$ dependence with the forward $\pi^{0}$ one as the $p_{T}$ approached to 1 GeV/$c$. We present the first measurement of the very forward $\pi^{0}$ asymmetry, its analysis procedure and preliminary result. A future aspect to more precisely study the non-perturbative contribution will be also introduced.
We outline a strategy to compute deeply inelastic scattering structure functions using a hybrid quantum computer [1]. Our approach takes advantage of the representation of the fermion determinant in the QCD path integral as a quantum mechanical path integral over 0+1-dimensional fermionic and bosonic worldlines [2]. The proper time evolution of these worldlines can be determined on a quantum computer. While extremely challenging in general, the problem simplifies in the Regge limit of QCD, where the interaction of the worldlines with gauge fields is strongly localized in proper time and the corresponding quantum circuits can be written down. As a first application, we employ the Color Glass Condensate effective theory to construct the quantum algorithm for a simple dipole model of the $F_2$ structure function. We outline further how this computation scales up in complexity and extends in scope to other real-time correlation functions.
[1] N. Mueller, A. Tarasov, R. Venugopalan, arXiv:1908.07051
[2] A. Tarasov, R. Venugopalan, Phys Rev D100 (2019), 054007
The CJ (CTEQ-Jefferson Lab) Collaboration provides a global fit of parton distribution functions (PDFs) with a special emphasis on the large x region. The latest fit (CJ15) implemented deuteron nuclear corrections at the parton level, and included data that were sensitive specifically to the neutron. These nuclear corrections allow for a calculation of the F2 structure functions of the proton, deuteron, and neutron from PDFs. In this work we re-estimated the uncertainties in the DIS F2 data utilized in CJ15, and collected an extended set of existing high-precision, small Q2, large x DIS data from JLab 6 GeV experiments. We employed the CJ15 calculation to remove nuclear effects from deuteron data where the proton was available from the same experiment, and thereby constructed a global data set for the F2 neutron structure function. In this talk, we will present the extracted F2 neutron data sets, as well as applications such as new neutron excess (isoscalar) corrections and a comparison to lattice QCD.
We analyze within the JAM framework the impact on unpolarized parton distributions of heavy-flavor production measurements in deep inelastic scattering. In particular, we investigate the recent combined results of inclusive and heavy-flavor production cross sections at HERA, which impose additional constraints on the gluon and the sea-quark distributions at low $x$.
We present our study of proton structure functions in view of the CLAS12 experiments planned in the near future, which are to study electron scattering observables at a wide $Q^2$ range and with high precision in x. CLAS experiments have achieved major advances in the study of the $N^∗$ region of the electroproduction spectrum, and the data on electrocouplings of the many baryon resonances in the mass range up to 1.8 GeV showed consistency between the different meson channels.
We model the resonant contributions to inclusive electron scattering, using the electrocoupling data as input. Our results are thus based on the reliable extraction of the separate resonance contributions from exclusive reactions. The combination of the resonance
model with a non-resonant background based on Regge models enables for the first time a
combined description of the low and high-x regions of the proton structure functions. Understanding the transition between these regions is important for a precise extraction of the hadronic contribution to the proton Lamb shift and tests on quark-hadron duality.
Following our recent Monte Carlo determination of the pion’s PDFs from Drell-Yan (DY) and leading neutron electroproduction data, we extend the analysis by including effects from threshold resummation. At higher orders in the strong coupling, $\alpha_S$, large logarithmic corrections due to soft gluon emissions become important in the $q\bar{q}$ channel near threshold, which can be summed over all orders of $\alpha_S$. However, different prescriptions exist for how the threshold resummation is implemented, for instance, using varying levels of approximation in the Minimal Prescription and Borel Summation. We report the results of the first simultaneous fit to the valence, sea, and gluon distributions in the pion taking into account the ambiguities in the resummation calculations.
Latest results about searches for long-lived particles with the CMS experiments will be presented. Prospects for Run III and beyond will also be discussed.
Various theories beyond the Standard Model predict unique signatures which are difficult to reconstruct and for which estimating the background rates is also a challenge. Signatures from displaced decays anywhere from the inner detector to the muon spectrometer, as well as those of new particles with fractional or multiple values of the charge of the electron or high mass stable charged particles are all examples of experimentally demanding signatures. The talk will focus on the most recent results using 13 TeV pp collision data collected by the ATLAS detector. Prospects for HL-LHC will also be shown.
Rare and exotic decays of the Higgs boson provide a unique
window for the discovery of new physics, as the Higgs boson may couple to leptons in flavour violating or otherwise anomalous ways, or to hidden-sector states that do not interact under the Standard Model gauge transformations. This talk summarizes recent ATLAS searches for unexpected decays of the 125 GeV Higgs boson: enhanced rates of dimuon decay, decay to two different charged leptons, and decay to new light bosons, H -> aa, where the a-bosons decay to various final states. These searches use LHC collision data at sqrt(s) = 13 TeV collected by the ATLAS experiment in Run 2.
The presence of a non-baryonic dark matter (DM) component in the Universe is inferred from the observation of its gravitational interaction. If dark matter interacts weakly with the Standard Model (SM) it could be produced at the LHC. The ATLAS experiment has developed a broad search program for DM candidates, including resonance searches for the mediator which would couple DM to the SM. The results of recent searches on 13 TeV pp data, their interplay and interpretation will be presented. Prospects for HL-LHC will also be discussed.
The realisation of the LHeC and the FCC-eh at CERN require the development of the energy recovering technique in multipass mode and for large currents ${\cal O}(10)$ mA in the SRF cavities. For this purpose, a technology development facility, PERLE, is under design to be built at ICLab Orsay, which has the key LHeC ERL parameters, in terms of configuration, source, current, frequency and technical solutions, cryomodule, stacked magnets. In this talk we review the design and comment on the status of PERLE.
The Electron-Ion Collider will be the first collider to use both polarized electron beams and polarized proton and light ion beams. This will offer unique opportunities to study the structure of protons and nuclei and to answer fundamental questions in QCD.
The uncertainties on the polarization measurement translate directly into the uncertainties of final physics observables. Hence, a precise measurement of the hadron beam polarization and a good control of the uncertainties are critical for the success of the spin program at the EIC.
Contrary to the case of electron beam polarimetry, which uses physical processes derived from first principles that allow a high precision extraction of the electron beam polarization, for hadron beams no such process is available, and the currently best used methods rely on the process of elastic scattering in the Coulomb-Nuclear Interference (CNI) region, of which there are only effective models available.
The experience from RHIC, the only polarized proton collider, will be detailed and the challenges of the measurements at the EIC will be addressed. In particular, measurements of the present RHIC polarimeters and simulations of the future EIC polarimeters will be presented.
Higgs production cross sections at LHeC (FCC-eh) energies are as large (larger than) those at future Z-H $e^+e^-$ colliders. This provides alternative and complementary ways to obtain very precise measurements of the Higgs couplings, primarily from luminous, charged current DIS. Recent results for LHeC and FCC-eh are shown and their combination is presented with pp (HL-LHC) cross sections leading to precision comparable to the most promising $e^+e^-$ colliders. We will show the results for the determination of several signal strengths and couplings to quarks, leptons and EW bosons, and discuss the possibilities for measuring the coupling to top quarks and its CP phase, and the search for invisible decays.
The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will enable a spectrum of new or improved cold QCD measurements. With its excellent tracking and full calorimetry (hadronic and electromagnetic) in the central pseudo-rapidity region, sPHENIX provides excellent opportunities for the studies of the partonic structure and dynamics in nucleons and nuclei. This includes the studies of the polarized structure of the proton utilizing RHIC's polarized proton collisions. Measurements will also take advantage of RHIC's unique capability to collide polarized protons on nuclei, which provides novel opportunities to study nuclear effects with spin observables. A potential upgrade to sPHENIX with forward instrumentation could significantly enhance these physics capabilities, expanding the probed kinematic range to lower and higher parton momentum fraction x. The cold QCD nuclear physics program for the proposed sPHENIX midrapidity detector as well as the enhanced program enabled with forward upgrades will be presented. The ongoing R&D work for the forward instrumentation will be discussed.
The confinement of quarks and gluons, the building blocks of all visible matter, is perhaps the ultimate example of quantum entanglement. Inside nucleons they are not just correlated, they do not even exist as isolated states. However, in the parton model formulated by Bjorken, Feynman, and Gribov, the partons are viewed by an external hard probe as independent when the nucleon is boosted to an infinite-momentum frame. Therefore, the parton probed by a virtual photon is causally disconnected from the rest of proton. It has been recently proposed that this apparent paradox can be resolved by quantum entanglement of partons, possibly manifesting itself in observables related to hadron multiplicities. In this talk, new experimental data on charged particle multiplicity distributions are presented, covering the kinematic ranges in momentum transfer $5< Q^2< 100$ GeV$^2$ and inelasticity $0.0375< y< 0.6$. The data were recorded with the H1 experiment at the HERA collider in positron-proton collisions at a centre-of-mass energy of 320 GeV. Charged particles are counted with transverse momenta $P_T>150$ MeV and pseudorapidity $-1.2< \eta<1.6$ in the laboratory frame, corresponding to high acceptance in the current hemisphere of the hadronic centre-of-mass frame. Charged particle multiplicities are reported on a two-dimensional grid of $Q^2$, $y$ and on a three-dimensional grid of $Q^2$, $y$, $\eta$. The observable is the probability $P(N)$ to observe $N$ particles in the given $\eta$ region. The data are confronted with predictions from Monte Carlo generators, and with a simplistic model based on quantum entanglement and strict parton-hadron duality.
The production of prompt isolated photons and jets at hadron colliders provides stringent tests of perturbative QCD and can be used to evaluate the probability density functions of partons in the proton. In this talk, we present the measurements of the isolated-photon plus two jets and the inclusive isolated-photons cross sections, both measured using proton-proton collision data collected by the ATLAS experiment at √s=13 TeV. The results are compared with state-of-the-art theory predictions, indicating several interesting discrepancies. If available, a measurement of event shape variables calculated using hadronic jets at √s=13 TeV will be presented. The measurement is compared to predictions by Monte Carlo event generators and results show discrepancies for some topologies.
We develop a systematic treatment of heavy-flavor hadroproduction in the framework of the General-Mass Variable-Flavor-Number Scheme (GM-VFNS). By following the idea of the Simplified-ACOT-$\chi$ Scheme in Deep Inelastic Scattering (DIS), we categorize the open heavy-flavor diagrams into Flavor Excitation (FE) and Flavor Creation (FC) contributions. In order to avoid double counting, overlapping contributions are subtracted using the collinear splitting approximation. The FC terms are extracted from the Fixed-Flavor-Number Scheme (FFNS), while the FE and Subtraction (SB) terms involve an initial heavy-flavor quark scattering with another parton (a light quark or gluon). We introduce a Massive Phase Space (MPS) for the FC and SB terms, which accounts for the threshold effect of massive heavy-flavor quarks. We dub this novel approach the ``S-ACOT-MPS'' scheme. The MPS regulates the singular behavior of the FE and SB (differential) cross sections in the limit $p_{T}\to 0$, and stabilizes their cancellation, thus reducing the S-ACOT-MPS scheme to the FFNS smoothly. Our numerical results demonstrate good agreement with LHCb data on $B^{\pm}$ production at 7 and 13 TeV.
In order to perform precise Standard Model measurements or to search for new physics phenomena at hadron colliders, it is important to have a good understanding of not only the short-distance hard scattering process, but also of the accompanying activity – collectively termed the underlying event. In this talk we present a study of the underlying event activity in events containing a Z-boson in √s=13 TeV data collected by the ATLAS experiment. Unfolded differential cross sections are presented for charged particle multiplicity and charged particle transverse momentum in regions of azimuth measured with respect to the Z-boson direction. If available, a study of the underlying event activity will be also presented for events where strange particles are identified in √s=13 TeV data. In both measurements, the data are compared to a wide variety of predictions from Monte Carlo event generators.
In this talk, we will present recent results on ultra-peripheral heavy-ion collisions with the CMS detector. This will include measurements on vector meson photoproduction in ultra-peripheral pPb and PbPb collisions, as well as light-by-light scattering measurements, and new studies of exclusive processes in photon-induced interactions to study low-x QCD dynamics. In addition, recent results on exclusive pi+pi- production in proton-proton collisions will also be shown.
Ultra-relativistic heavy ion collisions are expected to produce some of the strongest magnetic fields ($10^{13}-10^{16}$ Tesla) in the Universe[1].
These intense electromagnetic fields have been proposed as a source of linearly-polarized, quasi-real photons[2] that can interact via the Breit-Wheeler process to produce $e^+e^-$ pairs[3]. Demonstration that these photons are linearly polarized provides a precision tool for the study of open questions in Quantum Chromodynamics.
In this talk we present STAR measurements of $e^+e^-$ pair production and diffractive photo-production of the $\rho^0$-meson (and direct $\pi^+\pi^-$ pairs) in ultra-peripheral Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The pairs produced in the $\gamma\gamma \rightarrow e^+e^-$ process display a striking 4th-order azimuthal modulation which is a direct result of vacuum birefringence[4,5].
Using the same technique we present measurements of azimuthal modulations in $\pi^+\pi^-$ pairs from diffractive photo-production of the $\rho^0$ and of direct $\pi^+\pi^-$ pairs.
The measured $\pi^+\pi^-$ pairs reveal a similar 4th-order azimuthal modulation. We will discuss the implications of these measurements for the study of gluon transverse momentum dependent (TMD) distributions within nuclei[6,7] at existing experiments and at a future Electron Ion Collider.
[1] V. Skokov, A. Illarionov, and V. Toneev. International Journal of Modern Physics A 24 (2009): 5925–32.
[2] C. Weizsäcker, Zeitschrift für Physik 88 (1934): 612–25.
[3] G. Breit and J. A. Wheeler. Physical Review 46 (1934): 1087
[4] L. Cong, J. Zhou, and Y. Zhou. (2019). arxiv:1903.10084v1
[5] Heisenberg, W., and H. Euler. Zeitschrift für Physik, (1936) arXiv: physics/0605038
[6] J. Collins, and D. Soper. Nuclear Physics B 194 3 (1982): 445–92.
[7] A. Metz, and J. Zhou. Physical Review D 84 5 (2011).
The azimuthal decorrelation angle between the leading jet and scattered lepton in deep inelastic scattering is studied with the ZEUS detector at HERA. The data was taken in the HERA II data-taking period and corresponds to an integrated luminosity of 330 pb$^{-1}$. Azimuthal angular decorrelation has been proposed to study the $Q^2$ dependence of the evolution of the transverse momentum distributions (TMDs) and understand the small-$x$ region, providing unique insight to nucleon structure. Previous decorrelation measurements of two jets have been performed in proton-proton collisions at very high transverse momentum; these measurements are well described by perturbative QCD at next-to-leading order. The azimuthal decorrelation angle obtained in these studies shows good agreement with predictions from Monte Carlo models including leading order matrix elements and parton showers.
An important phenomenological consequence of the phenomenon of gluon saturation is the suppression of back-to-back hadron and jet pairs produced in the forward region of pA collisions. We present a new calculation of this process within the dilute-dense formalism of the color glass condensate (CGC) effective theory. Following Ref. [1], we collide a large-$x$, dilute probe, described in terms of parton distribution functions, off a dense target, described in terms of transverse momentum dependent (TMD) gluon distributions, whose small-$x$ evolution we calculate using rcBK evolution. We then couple this cross section with the formalism introduced in Ref. [2] to implement in an analytically-controlled way the radiation of soft gluons (Sudakov resummation) from the initial and the final state.
We first apply this CGC+Sudakov framework to the production of forward di-jets at high-$p_t$ in pp and pA collisions. We use the same kinematic cuts and collision energy as in a recent analysis by the ATLAS collaboration [3]. We find that the suppression of the di-jet yield at $\Delta\phi=\pi$, predicted by gluon saturation, is essentially washed out by a strong effect of broadening induced by the radiation of soft gluons. Compatibly with ATLAS data, we find that the nuclear modification factor for forward high-$p_t$ dijets is at best of order $R_{pA}\approx 0.9$.
Motivated by this result, we propose to study the production of forward dihadrons (pions) at lower, though moderate, $p_t$($\approx$10 GeV). We find that, in this case, the suppression of back-to-back pairs genuinely predicted by gluon saturation survives the broadening due to the Sudakov resummation. We indeed obtain $R_{pA}\approx 0.75$ at $\Delta\phi = \pi$ using kinematic cuts compatible with the proposed FoCal upgrade of the ALICE detector. We conclude that forward dihadrons at high $p_t$ provide a sensitive probe of gluon saturation at LHC.
[1] J. L. Albacete, G. Giacalone, C. Marquet and M. Matas, https://arxiv.org/abs/1805.05711
[2] A. Stasto, S-Y. Wei, B-W. Xiao, and F. Yuan https://arxiv.org/abs/1805.05712
[3] ATLAS Collaboration https://arxiv.org/abs/1901.10440
The interplay between the small x limit of QCD amplitudes and QCD factorization at moderate x has been studied extensively in recent years. It was finally shown that semiclassical formulations of small x physics can have the form of an infinite twist framework involving Transverse Momentum Dependent (TMD) distributions in the eikonal limit. In this work, we demonstrate that small x distributions can be formulated in terms of transverse gauge links. This allows in particular for direct and efficient decompositions of observables into subamplitudes involving gauge invariant suboperators which span parton distributions. The application to Dijet production in eA collisions will be discussed beyond the correlation limit as well as a strategy to compute finite energy corrections.
We present our recent results on the QCD evolution of the Jaffe-Manohar orbital angular momentum distributions. We discuss both $Q^2$ evolution and small-$x$ evolution.
Deep Inelastic Scattering (DIS) and especially Semi-Inclusive Deep Inelastic Scattering (SIDIS) are leading processes in the study of hadron structure. The theoretical treatments of these processes involve approximations which only hold true in specific regions of kinematics, each region corresponding to a different physical picture. Ratios have been defined to be representative of terms which are approximated as small in well known factorization theorems. Using these ratios, we define a way to quantify confidence in the proximity to a given factorization region, given assumptions about parton properties. Ultimately, these results will for the first time give a well defined methodology for determining confidence that some kinematical configuration may be described in terms of TMDs, given assumptions about partonic kinematics.
We study the semi-inclusive production of hard, isolated photons in unpolarized and polarized lepton-proton collisions, i.e., $\ell p\to \ell\gamma X$. We analyze the transverse nucleon single-spin asymmetry within the collinear twist-3 formalism in perturbative QCD to leading order accuracy (LO). We find that this spin asymmetry is generated by twist-3 dynamical quark-gluon-quark ($qgq$) correlations in the nucleon through so-called soft-fermion pole and hard pole contributions. In particular, the latter are of interest as they -in principle- allow for a point-by-point scan of the support of the dynamical $qgq$ twist-3 matrix elements $F_{FT}(x,x^\prime)$ and $G_{FT}(x,x^\prime)$ in lepton-nucleon scattering experiments.
The main focus of this talk is our recent work [1] on transverse single spin asymmetry (SSA) in semi-inclusive DIS in a collinear twist-3 framework. I will explicitly demonstrate that a genuinely new contribution containing the $g_T$ distribution function (alongside the kinematical and the dynamical Qiu-Sterman functions) is first seen at two loops. The phase required for a non-zero SSA from $g_T$ is generated by a mechanism completely distinct from the familiar Qiu-Sterman and Collins contributions as it originates purely within the parton-level cross section. I will explain the structure of our all-order gauge invariant result for the hadronic tensor in SIDIS and show a complete set of gauge invariant diagrams that contribute at two loops. Finally, I will discuss collinear factorization in our final formula for the $g_T$ contribution as well as its phenomenological implications.
[1] S. B., Y. Hatta, H.-N. Li and D.-J. Yang, Phys.Rev. D100 (2019) no.9, 094027.
Measurements of the total and differential top-quark pair production cross sections in proton- proton collisions at 13 TeV with the ATLAS detector at the Large Hadron Collider are presented. The inclusive measurement reaches a precision of 2.4 %, well below the uncertainty of predictions at next-to-next-to-leading order in QCD. The measurement is performed in the di-lepton channel, requiring a high-pT electron and muon. The experimental uncertainties due to the identification of b-quark jets are constrained in-situ by data. The total cross-section is compared to predictions by different sets of parton distribution functions (PDFs) and is used to determine the top-quark mass. Differential measurements of the kinematic properties of the two leptons are also performed. The high sensitivity of some distributions to PDFs is demonstrated. The distributions are also compared to predictions by several Monte Carlo event generator setups.
We discuss the impact of top-quark pair production data on the CT18 PDFs family.
In particular, we discuss the individual impacts of differential ttbar cross section measurements at 8 TeV collision energy from CMS and ATLAS which have been analyzed using different statistical frameworks (ePump and PDFSense) to assess their impact on PDFs before the global fit. We discuss tensions between ttbar observables and the different pulls they lead on the gluon in the global fit to determine the CT18 PDFs. The interplay of ttbar measurements with jet production data is also analyzed.
The differential cross section and charge asymmetry for inclusive W boson production at sqrt{s} = 13 TeV is measured for the two transverse polarization states as a function of the W boson absolute rapidity. The measurement uses events in which a W boson decays to either an electron or a muon and a neutrino. The data sample of proton-proton collisions recorded with the CMS detector at the LHC in 2016 corresponds to an integrated luminosity of 36 fb-1. The absolute differential cross section, and its value normalized to the total inclusive W boson production cross section, are measured over the rapidity range |Y_W| < 2.5. In addition, the W boson double-differential cross section, d^2sigma/dpT d|eta|, and the charge asymmetry, are measured as a function of the charged lepton transverse momentum and pseudorapidity.
Over the past several years, parton distribution functions (PDFs) have become more precise. However there are still kinematic regions where more data are needed to help constrain global PDF extractions, such as the ratio of the sea quark distributions $\bar{d}$/$\bar{u}$ near the valence region. Furthermore, current measurements appear to suggest different high-$x$ behaviors of this ratio. The $W$ cross-section ratio ($W^+$/$W^-$) is sensitive to the unpolarized quark distributions at large $Q^2$ set by the $W$ mass. Such a measurement can be used to help constrain the $\bar{d}$/$\bar{u}$ ratio. The STAR experiment at RHIC is well equipped to measure the leptonic decays of $W$ and $Z$ bosons, in the pseudorapidity range $\left(-1.0 < \eta < 1.5 \right)$, produced in proton-proton collisions at $\sqrt{s}$ = 500/510 GeV. These cross sections and their ratios are sensitive to quark and antiquark distributions in the $x$-range $0.1 < x < 0.3$. This talk will present preliminary results from the 2011-2013 RHIC runs, which total about 350 pb$^{-1}$ of integrated luminosity. Measurements of the differential $W$ and $Z$ cross sections and the $W^+$/$W^-$ cross-section ratio as a function of the lepton's pseudorapidity, as well as the $W/Z$ cross-section ratio and total $W$ and $Z$ cross sections will be shown.
High-energy neutrinos represent a key pillar of multi-messenger astronomy and offer significant opportunities to advance fundamental physics. The interpretation of the results from high-energy neutrino detection experiments requires a good understanding of the attenuation processes that they undergo as they travel through the Earth. Here we present a novel framework, NuPropEarth, to evaluate the impact of matter effects in the propagation of high energy neutrinos. Precise calculations of the neutrino-nucleon cross- sections with state-of-the-art perturbative and non-perturbative inputs are provided by the HEDIS module of GENIE. We adopt proton parton distribution functions (PDFs) constrained by charm production from LHCb that can be reliable applied down to small values of Bjorken x. We compare our calculations with other publicly available tools such as NuFate and NuTauSim, and trace back the origin of eventual differences. We quantify the dependence of the resulting neutrino attenuation with respect to the Earth model, the incidence angle, and the spectral index of the incoming flux. For the first time, we assess the impact of nuclear corrections in the attenuation rates and demonstrate that these now represent the dominant source of theoretical uncertainties. Our results provide an important contribution to the scientific harvest of ongoing and next-generation high-energy neutrino detection experiments.
The tremendous phenomenological success of the Standard Model (SM) suggests that its flavor structure and gauge interactions may not be arbitrary but should have a fundamental first-principle explanation. In this work, we explore how the basic distinctive properties of the SM dynamically emerge from a unified New Physics framework tying together both flavour physics and Grand Unified Theory (GUT) concepts. This framework is suggested by the gauge Left-Right-Color-Family Grand Unification under the exceptional E8 symmetry that, via an orbifolding mechanism, yields a supersymmetric chiral GUT containing the SM. Among the most appealing emergent properties of this theory is the Higgs-matter unification with a highly-constrained massless chiral sector featuring two universal Yukawa couplings close to the GUT scale. At the electroweak scale, the minimal SM-like effective field theory limit of this GUT represents a specific flavored three-Higgs doublet model consistent with the observed large hierarchies in the quark mass spectra and mixing already at tree level.
Most recent results on searches for supersymmetric (SUSY) particles decaying to final states containing high energy photon(s) are presented. The searches are based on data collected at the center-of-mass energy of 13 TeV in proton-proton collisions recorded by the CMS detector. Photons may arise directly from a decay of a SUSY particle or due to the decay of a Higgs boson created in the SUSY decay chain. The studies consider several interpretations in both the weak and the strong production channels.
Many theories beyond the Standard Model predict new phenomena, such as Z’ and leptoquarks, in final states containing bottom or top quarks. Such final states offer great potential to reduce the Standard Model background, although with significant challenges in reconstructing and identifying the decay products and modelling the remaining background. The recent 13 TeV pp results, along with the associated improvements in identification techniques, will be reported.
Supersymmetry (SUSY) provides elegant solutions to several
problems in the Standard Model, and searches for SUSY particles are an important component of the LHC physics program. This talk will present the latest results from searches conducted by the ATLAS experiment, covering both strong and electroweak SUSY particle production processes. The searches target multiple final states and different assumptions
about the decay mode of the produced SUSY particles, including searches for both R-parity conserving models that predict dark matter candidates and R-parity violating models that typically lead to high-multiplicity final states without large missing transverse momentum. The searches are interpreted as constraints on a variety of SUSY models as well as
simplified associated-production dark matter models.
The scattering and neutrino detector (SND) at the LHC will measure for the first time neutrino properties from $pp\rightarrow \nu X$ and search for Dark Matter in an unexplored energy and pseudo-rapidity range. It will be located in the TI18 tunnel, which is ideal due to the low environmental and machine-induced background. The detector will measure the neutrino energy and identify all three neutrino species in an unprecedented energy domain (between 350 GeV and few TeV). The experiment will be off-axis and cover a pseudo-rapidity range from 7.2 < $\eta$ < 8.8, meaning the incoming neutrinos stem mainly from charm decays. It will comprise a nuclear emulsion target interleaved with a scintillating fibre tracker, a timing detector with a resolution less than 50 ps, and a downstream muon identification system. An upstream veto timing detector will filter out charged particles. The neutrino flavour will be identified by the charged lepton at the primary vertex: electrons and taus will be identified within the emulsion while the muons will be identified in the muon detector. Dark Matter will be identified by its nuclear recoil within the emulsion material. The energy of incident particles will be reconstructed by measuring the energy of electrons and hadrons in a calorimetric way with scintillator fibre planes.
Tau neutrino properties are not well known in comparison to those of muon or electron neutrinos. The tau neutrino interaction cross-section is known with large uncertainties. In particular, measured by the DONuT experiment in 2008, it has about 30% statistical error and systematical error of about 50% due to a poor knowledge of the tau neutrino flux in this beam dump experiment. Precise measurement of tau neutrino interaction cross-section will allow to test the Lepton Flavour Universality (LFU) of Standard Model in neutrino interactions. Several results for B-meson decays (LHCb, Babar, BelleII) demonstrated hints of possible LFU violation in modes with tau lepton could be due to Physics Beyond Standard Model effects. Accurate measurement of the tau neutrino interaction cross section is also needed for the future neutrino experiments. The tau neutrinos are produced in the Ds meson decays: Ds → τ + ντ, with further decay τ→ X + ντ . DsTau experiment has been proposed to measure the Ds production differential cross-section in proton- tungsten interaction. This will allow reducing of the uncertainty due to the tau neutrino flux in the DONUT result from 50% to 10% . The peculiar Ds cascade decay topology ("double kink") in a few mm range will be detected by nuclear emulsion tracker thanks to its excellent spatial resolution (~50nm). Large amount of charm decay events (~10^5) are expected to be detected as well, providing interesting by-product studies, in particular a search of intrinsic charm in a proton. In 2016 and 2017, and in 2018, a pilot sample was collected at CERN SPS and processed in 2019. Given the success of pilot test beam and encouraging results of data analysis, CERN approved the DsTau project as a new experiment NA65. Main data sample (x10 more) will be collected in 2021-22. In this talk, the status, prospects of NA65 as well as the results of the pilot run are presented.
In the context of the Physics Beyond Colliders initiative at CERN, the COMPASS++/AMBER proto-collaboration recently submitted a proposal to the SPSC in which a broad experimental programme of measurements at the M2 beam line of the CERN SPS is described. It addresses fundamental issues leading to significant improvements in our understanding of strong interactions in the medium and long-term future. The proposed measurements cover a wide range in the squared four-momentum transfer $Q^2$. At lowest values of $Q^2$, a determination of the proton charge radius through elastic muon-proton scattering is planned, at intermediate $Q^2$ a spectroscopy of mesons and baryons by using dedicated meson beams, and at high $Q^2$ (i.e. small distances), studies of the structure of mesons and baryons via the Drell-Yan process are forseen.
Beyond the CERN accelerators Long Shutdown-3, an upgrade of the M2 beam line by installing a radio-frequency separation for kaon and antiproton beams of high energy and high intensity is proposed to further unique measurements that cannot be performed elsewhere.
In the talk an overview of the full project which is expected to stretch across the next 10 to 15 years will be presented.
The sPHENIX detector currently under construction at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) is designed to significantly advance studies of the microscopic nature of the Quark
Gluon Plasma. With a multi-year physics program beginning in 2023, sPHENIX employs state-of-the-art detector technologies and will fully exploit the highest planned RHIC luminosities. The experiment
incorporates a high rate DAQ to collect data from full azimuth vertexing, tracking, and electromagnetic and hadronic calorimetry over the pseudorapidity range |η|<1.1 and will deliver unprecedented data
sets for a wide variety of multi-scale measurements at RHIC, including studies of jet modification, upsilon suppression and open heavy flavor production in p+p, p+Au, and Au+Au collisions. In this talk, we will present an overview of the planned sPHENIX QGP physics program and progress toward the realization of the detector.
Two-particle azimuthal correlations have been measured in neutral current deep inelastic ep scattering with virtuality $Q^2 > 5$ GeV$^2$ at a centre-of-mass energy $\sqrt{s}=318$ GeV recorded with the ZEUS detector at HERA. The correlations of charged particles have been measured in the range of laboratory pseudorapidity $-1.5 < \eta < 2$ and transverse momentum $0.1 < p_T < 5$ GeV and event multiplicities $N_{\rm ch}$ up to six times larger than the average $\langle N_{\rm ch}\rangle \approx 5$. The two-particle correlations have been measured in terms of the angular observables $c_n\{2\}=\langle\langle\cos n\Delta\phi\rangle\rangle$, where $n$ is between 1 and 4 and $\Delta\phi$ is the relative azimuthal angle between the two particles. The correlations observed in HERA data do not indicate the kind of collective behaviour recently observed at the highest RHIC and LHC energies in high-multiplicity hadronic collisions. Available Monte Carlo models of deep inelastic scattering, tuned to reproduce inclusive particle production, provide a qualitative description of the HERA data.
The study of hadron production and anisotropic flow are key to the understanding of the medium produced in heavy ion collisions and its event-by-event fluctuations. Recent results in small systems both at RHIC and LHC support the formation of such medium at those scales.
PHENIX has measured the spectra of charged and identified particles for several small systems and at various energies, as well as their 2nd and 3rd anisotropic flow coefficients. These results show a remarkable dependence of the flow amplitude with initial geometry which is fully described by current viscous hydrodynamic models.
ATLAS measurements of flow harmonics ($v_n$) and their fluctuations in Pb+Pb and Xe+Xe collisions covering a wide range of transverse momenta, pseudorapidity and collision centrality are presented. The measurements are performed using data from Xe+Xe collisions at 5.44 TeV and Pb+Pb collisions at 2.76 and 5.02 TeV. The $v_{n}$ are measured up to $n=6$ using the two-particle correlations, multi-particle cumulants, and scalar product methods. The $v_{n}$ measurements are also performed using a non-flow subtraction technique that was developed for flow measurements in $pp$ and $p$+Pb collisions. This non-flow subtraction is found to have a significant effect on the measured $v_n$ at high-$p_T$ and in peripheral collisions. A universal scaling in the $p_{T}$ dependence of the $v_{n}$ is observed for both systems. Measurements of correlations between the $v_n$ for different order $n$, studied with three- and four-particle mixed-harmonic cumulants, are also presented, and contributions to these correlations from ``centrality fluctuations'' are also discussed.
Measurements of longitudinal flow decorrelations involving two- and four-particle correlations for $v_{2}$ and $v_{3}$ in Xe+Xe and Pb+Pb collisions are also presented and compared with predictions from theoretical calculations. The four-particle decorrelation is found to not factorize as a product of two-particle decorrelations. The ability of such measurements to distinguish between different models of initial geometry and to reduce the uncertainty in determining the effective shear-viscosity to entropy-density ratio of the QGP is demonstrated.
This talk presents multiple recent ATLAS measurements form the ATLAS collaboration that study features of the azimuthal distributions for charged particles in $pp$ and $p$+Pb collisions. The measurement of the azimuthal anisotropy of charged hadrons in $p$+Pb collisions up to a transverse momentum of 50 GeV are presented. In A+A collisions non-zero flow coefficients at high-$p_{T}$ are understood to arise from the path-length dependent energy loss of jets. Thus, these measurements in $p$+Pb collisions can provide information on the origin of these collective phenomena. To further assess properties of the azimuthal anisotropy in $p$+Pb collisions, the correlation between the mean transverse momentum and the magnitudes of the flow harmonics is also measured. The measurements are performed in 5.02 TeV $p$+Pb collisions for several intervals of the charge particle transverse momentum and as a function of the event-multiplicity. The measured correlations are compared to similar measurements in Pb+Pb collisions.
Measurements of correlations in ultra-peripheral Pb+Pb collisions, in which the nuclei do not interact hadronically, but a quasi-real photon from the EM field of one nucleus can interact with the other nucleus are also presented. These photons may reach energies up to 80 GeV and readily fluctuate into vector-meson configurations, resulting in these collisions effectively being vector-meson+Pb collisions.
Prior measurements of two-particle correlations in $pp$ collisions have demonstrated long-range azimuthal correlations between charged particle pairs. The impact-parameter dependence of these correlations are studied in events containing a $Z$-boson, which acts as an independent handle on the impact parameter of the $pp$ collision. Measurements of the $p_{T}$ and event-multiplicity dependence of the azimuthal anisotropy in such $Z$-tagged $pp$ collisions at 8 and 13 TeV are also presented. Measurements of the azimuthal anisotropy of muons from heavy-flavor decays in $pp$ collisions at 13 TeV, which may further elucidate the origin of these correlations in $pp$ collisions, are also presented.
Scattering amplitudes have always been essential to compute cross sections and production rates at colliders. In the last few years, though, there has been terrific progress in understanding the rich mathematical structure of scattering amplitudes, the more so in specific kinematic regions, like the Regge limit. In this talk, I will outline what we have learnt about the weak-coupling expansions of amplitudes in quantum field theories, and then specify it to the Regge limit of QCD and of N=4 super-Yang-Mills theory.
We propose an all-loop expression for scattering amplitudes in planar N=4 super Yang-Mills theory in multi-Regge kinematics valid for all multiplicities, all helicity configurations and arbitrary logarithmic accuracy. Our expression is arrived at from comparing explicit perturbative results with general expectations from the integrable structure of a closely related collinear limit. A crucial ingredient of the analysis is an all-order extension for the central emission vertex that we recently computed at next-to-leading logarithmic accuracy. As an application, we use our all-order formula to prove that all amplitudes in this theory in multi-Regge kinematics are single-valued multiple polylogarithms of uniform transcendental weight.
We analyze the possibilities for the study of inclusive diffraction offered by future electron-proton/nucleus colliders in the tera-electron-volt regime, the Large Hadron-electron Collider (LHeC) as an upgrade of the HL-LHC, and the Future Circular Collider in electron-hadron mode. Compared to ep collisions at HERA, we find an extension of the available kinematic range in x by a factor of order 20 and of the maximum Q2 by a factor of order 100 for LHeC, while the Future Circular Collider (FCC) version would extend the coverage by a further order of magnitude both in x and Q2. This translates into a range of the available momentum fraction of the diffractive exchange with respect to the hadron (ξ), down to 10-4–10-5 for a wide range of the momentum fraction of the parton with respect to the diffractive exchange (β). Using the same framework and methodology employed in previous studies at HERA, considering only the experimental uncertainties and not those stemming from the functional form of the initial conditions or other ones of theoretical origin, and under very conservative assumptions for the luminosities and systematic errors, we find an improvement in the extraction of diffractive parton densities from fits to reduced cross sections for inclusive coherent diffraction in ep by about an order of magnitude. For eA, we also perform the simulations for the Electron Ion Collider. We find that an extraction of the currently unmeasured nuclear diffractive parton densities is possible with accuracy similar to that in ep.
Quantum tomography reconstructs higher dimensional features of quantum mechanical
systems from lower dimensional experimental information. The method is practical and directly processes experimental data while bypassing field-theoretic formalism. Quantum tomography can probe entanglement while avoiding model assumptions such as factorization. We review recent work applying quantum tomography to systematic analysis of collider reactions, including the inclusive production of dijets.
The proton as a quantum object is in a pure state and is described by a completely coherent wave function with zero entropy. On the other hand in high energy experiments (DIS) when probed by a small external probe, it behaves like an incoherent ensemble of (quasi-free)
partons.
In this talk, we define the "entropy of ignorance" which quantifies the entropy associated with ability to perform only a partial set of measurement on a quantum system. For a parton model the entropy of ignorance is equal to a Boltzmann entropy of a classical system of partons. We analyze a calculable model used for describing low x gluons in Color Glass Condensate approach, which has similarities with the parton model of QCD. In this model we calculate the entropy of ignorance in the particle number basis as well as the entanglement entropy of the observable degrees of freedom. We find that the two are similar at high momenta, but differ by a factor of order unity at low momenta. This holds for the Renyi as well as von Neumann entropies. We conclude that the entanglement does not seem to play an important role in the context of the parton model.
While significant steps toward the formal definition of quark TMDs and their extraction from experimental data through global fits has been made in the last years, the gluon-TMD field represents a largely unexplored territory. Pursuing the goal of extending our knowledge of this sector, we present analytic expressions for all $T$-even gluon TMDs at twist-2, calculated in a spectator model for the parent nucleon. At variance with respect to previous works, our approach encodes a flexible parametrization for the spectator-mass spectral density, allowing us to improve the description in the small-$x$ region.
We build a common framework where valence, sea quark and gluon densities are concurrently generated. Our results can be used to predict the behavior of observables sensitive to TMD dynamics.
Our understanding of the origin of the nucleon spin remains incomplete. Determining the partonic orbital angular momentum (OAM) contributions is particularly challenging experimentally. One possible signature for the partonic OAM would be detection of a non-zero Sivers effect, which characterizes the correlation between the transverse momentum of a parton ($\vec k_T$) and the transverse spin ($\vec S$) of its proton, moving in the longitudinal ($\vec p$) direction. Experimentally, the Sivers function can be accessed by searching for a preference in the bisector ray of di-jet transverse opening angle, which reverses direction when the beam polarization direction is flipped. A previous effort by STAR using 1~pb$^{-1}$ of $p$+$p$ data taken in 2006 at $\sqrt{s}$ = 200 GeV did not find a significant effect due to limited statistical precision. In 2012 and 2015, STAR accumulated much larger datasets ($\sim$33 times the di-jets after event selection) at $\sqrt{s}$ = 200 GeV. Moreover, a new technique has been implemented to tag the flavor of the fragmenting partons, to avoid cancellation between $u$ and $d$ quark effects, which are expected to have opposite signs. In this talk, a preliminary result of the measurement of Sivers asymmetries using STAR 2012 and 2015 $p$+$p$ data at $\sqrt{s}$ = 200 GeV will be reported.
Sivers function is a fundamental TMD which allows to investigate the 3D structure of polarized nucleons. We present a recent extraction of this function from azimuthal asymmetries in semi-inclusive DIS. This study includes for the first time TMD evolution contributions and a parametrization of unpolarized TMDs determined directly from data. Through this analysis we can obtain a tomography of the internal structure of nucleons in momentum space. Finally, We discuss a possible way to determine quark angular momentum through its relation with the extracted distribution.
In this talk, I will introduce our study on the probing transverse momentum dependent gluon Sivers function in open charm and charm jets production at the future EIC. We derive the theoretical framework to calculate heavy-quark pair and heavy jet pair production in the small transverse momentum region. Based on the factorization and resummation formula, we resum large logarithms in the small qT region and present the theoretical predictions for the single-spin asymmetry.
The differential cross section measurements of the production of a pair of opposite-charged leptons as a function of pt and phi* in various bins of its invariant mass M are presented. The results are obtained using proton-proton collision data recorded with the CMS detector at the LHC. Measurements are also compared to state-of-the-art generators as well as TMD based predictions.
The leading-twist azimuthal asymmetries in the pion induced Drell-Yan process in the COMPASS kinematics are calculated considering any polarization of the proton target. The calculations are performed at tree level in the framework of TMD factorization using the predictions from the light front constituent model. The results are compared to the available COMPASS data, and predictions for not yet measured asymmetries are presented whose confrontation with future data will allow us to test further the approach.
Transverse momentum dependent (TMD) parton distributions enter QCD factorisation formulas which include resummation and nonperturbative contributions to non-inclusive collider observables such as Drell-Yan differential cross sections. Recently, a parton branching (PB) formalism has been proposed for the evolution of TMDs, given in terms of Sudakov form factors and splitting functions. This approach has been matched with next-to-leading hard-scattering matrix elements and applied to obtain predictions for Drell-Yan qT and phi^star differential distributions.
In this talk I describe the basic elements of the PB method and present ongoing work to extend the method towards including the transverse momentum dependence in the splitting functions. To this end, I briefly review the notion of TMD splitting functions which has been used for a long time in the context of high-energy resummation, and describe the implementation of these functions in the PB evolution method. I discuss in detail the collinear (DGLAP) and high-energy (BFKL) limits of the TMD splitting functions. I illustrate the effects of TMD contributions with numerical simulations, and the prospects for using TMD splitting functions in phenomenological predictions.
We compute DIS structure functions using off-shell matrix elements based on kT-factorization. The obtained results are used together with parton branching evolution and HERA data in order to fit unintegrated (transverse momentum dependent) parton distributions. This allows us to have a consistent framework where off-shellness of initial partons is treated both in parton evolution and in matrix elements. It also gives us a unique opportunity to estimate the importance of accounting for the off-shellness in matrix elements.
We present a new determination of Transverse Momentum Dependent (TMD) parton distributions obtained with the Parton Branching method. The PB TMDs are extracted from fits to precision DIS data using DGLAP splitting functions at leading and higher order.
In addition the fit sensitivity to dynamical resolution scales on TMD evolution in different kinematical region of x and Q2 will be investigated.
The Large Hadron Collider (LHC) has been successfully delivering proton-proton collision data at the unprecedented center of mass energy of 13 TeV. An upgrade is planned to increase the instantaneous luminosity delivered by LHC in what is called HL-LHC, aiming to deliver a total of about 3000/fb of data to the ATLAS detector at a center of mass energy of 14 TeV. To cope with the expected data-taking conditions ATLAS is planning major upgrades of the detector.
In this contribution we present an overview of the physics reach expected for a wide range of measurements of Standard Model physics at the HL-LHC for the ATLAS experiment, ranging from standard-candle processes as top mass measurement, to measurement of rare processes as multi-boson differential cross section measurements. Particular focus would be given to implications of vector boson scattering to the investigation of electroweak symmetry breaking.
Such studies formed the basis of the ATLAS Collaboration input to one of the chapters of the recent HL/HE-LHC Yellow-Report. An executive summary of this report was then submitted as input to the European Strategy process.
Nuclear and particle physics are both presently grappling with an array of fundamental questions, running from the dynamical origin of hadronic mass and spin on the one side, to high-energy tests of the Standard Model on the other. Given this situation, we expect a future DIS collider --- the Electron-Ion Collider (EIC) for which DOE recently announced CD-0 --- to play an essential role in addressing these and many other issues. The enormous power of the EIC will derive from its very high luminosity (~100 times that of HERA) and the relative phenomenological cleanliness of the DIS process itself, which will afford unprecedented resolution to visualize the wave functions and internal dynamics of hadrons and nuclei. In this talk, I will review the primary scientific objectives of the EIC program and survey the large impact it can be expected to have on a wide range of physics at higher energies, especially at the LHC.
The study of QCD has served as a unifying focus and a common ground for the disciplines of high-energy and nuclear physics, and for both phenomenological and formal studies in theoretical physics. We are embarking on a historic journey. Existing facilities, from JLab to the LHC, and the now-approved Electron-Ion Collider, will provide unprecedented opportunities and challenges to reach a new level of understanding of the visible universe. We can hope to answer questions we have learned to pose so far, and to realize fully the potential of these developing tools, new questions remain to be discovered.