DIS-2021 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.
Testing the couplings of the Higgs boson to leptons is important to understand the origin of lepton masses. This talk presents measurements of Higgs boson production in decays to two tau leptons or two muons based on pp collision data collected at 13 TeV.
The CMS experiment at LHC has performed the first measurement of the CP structure of the Yukawa coupling between the Higgs boson and tau leptons. The measurement is based on data collected in proton-proton collisions at sqrt(s) = 13 TeV during 2016-18, corresponding to an integrated luminosity of 137 fb^-1. The analysis utilizes the angular correlation between the decay planes of tau leptons produced in Higgs boson decays, where dedicated analysis techniques are used to optimise the reconstruction of tau decay planes. The measured value of CP mixing angle is 4 +/- 17^o, at 68% confidence level. The pure CP-odd hypothesis is excluded by 3.2 standard deviations. The analysis strategies and the results of the measurement are presented.
The CP structure of the Higgs boson in its coupling to the particles of the Standard Model is amongst the most important Higgs boson properties which have not yet been constrained with high precision. In this study, all relevant inclusive and differential Higgs boson measurements from the ATLAS and CMS experiments are used to constrain the CP-nature of the top-Yukawa interaction. The model dependence of the constraints is studied by successively allowing for new physics contributions to the couplings of the Higgs boson to massive vector bosons, to photons, and to gluons. In the most general case, we find that the current data still permits a significant CP-odd component in the top-Yukawa coupling. Furthermore, we explore the prospects to further constrain the CP properties of this coupling with future LHC data by determining tH production rates independently from possible accompanying variations of the tt̄H rate. This is achieved via a careful selection of discriminating observables. At the HL-LHC, we find that evidence for tH production at the Standard Model rate can be achieved in the Higgs to diphoton decay channel alone.
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, or 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 measurements exploiting the full Run 2 statistics. Recent constraints on new physics models derived from high mass searches in the WW channel are also presented.
We present results with soft-gluon resummation for the associated production of a single top quark and a Higgs boson. We present analytical results for the higher-order soft-gluon corrections and numerical results for the total cross section and top-quark transverse momentum and rapidity distributions at LHC energies.
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 interpretations.
The presentation will cover breakthroughs in detector technology in accelerator based and non-accelerator based particle physics experiments and facilities.
The Electron-Ion Collider (EIC) is a new, innovative, large-scale particle accelerator to be built at Brookhaven National Lab in the USA over the next 10 years. It will collide beams of polarized electrons with polarized beams of light ions, or with heavy ions, at high luminosity. The goal is to study the fundamental structure of nucleons and nuclei, and the theory of Quantum Chromodynamics that describes their interactions.
The ElC Users Group (EICUG) has recently undertaken a major effort to quantify the requirements of the future EIC detectors so that they can deliver the best possible science. A tremendous amount of work has gone into this project which included a large fraction of the community over the year 2020. It has culminated in the release of a Yellow Report summarizing all the findings.
During this presentation we will outline the contents of the Physics Volume of the EIC Yellow Report and highlight some key measurements that drive the most stringent detector requirements.
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 ${\mathcal O}(10)$ mA in the SRF cavities. For this purpose, a technology development facility, PERLE, is under design to be built at IJCLab 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.
We present predictions and projections for hadron-in-jet measurements and electron-jet azimuthal correlations at the future Electron-Ion Collider. These observables directly probe the quark transversity and Sivers parton distributions, the Collins fragmentation functions, and TMD evolution. This jet-based approach will allow us to avoid the convolution of TMD parton distributions and fragmentation functions, which limits the constraining power of SIDIS measurements. We explore the feasibility of these measurements with detector simulations.
The SPD (Spin Physics Detector) facility is meant to be a universal 4π detector at the new collider complex NICA at the Joint Institute for Nuclear Research (JINR, Russia). The main goal of the experiment is to study the polarized gluon structure of proton and deuteron in the production of charmonium, open charm and direct photons. At its initial stage, SPD will also focus on various unpolarized and spin-dependent effects in interactions of protons, deuterons and light nuclei. The detector will be equipped with a silicone vertex detector, straw-tube detector, time-of-flight system, electromagnetic calorimeters and a range system for muon identification. A solenoidal magnetic field of 1 T will be provided by six superconductive coils. A luminosity of 10^{32} s^{-1}cm^{-2} can be achieved for colliding p-p beams at the maximum interaction energy of sqrt(s) = 27 GeV. Both longitudinal and transverse beam polarization will be available. Conceptual Design Report (CDR) of the experiment was released by the collaboration in the winter 2021. The status of the experiment will be reviewed.
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 Conceptual Design Report update [1]. 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.
[1] LHeC Collaboration and FCC-he Study Group, P. Agostini et al., e-Print: 2007.14491 [hep-ex].
Threshold photoproduction of charmonium at JLab and EIC can be used to extract the distribution of mass inside the proton by using the scale anomaly of QCD and the multipole expansion. Theoretical analysis of this problem will be presented and confronted with the first experimental data from JLab.
The suppression of $J/\psi$ production caused by the color-screening effect in heavy-ion collisions is considered as an evidence of the creation of quark-gluon plasma. To interpret the observed suppression in heavy-ion collisions, a good understanding of its production mechanism in p+p collisions is needed. However, the production of $J/\psi$ in hadronic collisions remains not fully understood and requires further studies. Recently, $J/\psi$ production in jets was proposed as a useful observable to help explore the $J/\psi$ production mechanism, and to differentiate various $J/\psi$ production models.
In this talk, we will present the measurement of the fraction of charged jet transverse momentum ($p_{T}$) carried by the $J/\psi$ meson, z($J/\psi$) $\equiv$ $p_{T}(J/\psi)$/$p_{T}(jet)$, at mid-pseudorapidity ($|\eta|<1$) with kinematic cuts of $p_{T}(J/\psi)>$5 GeV/c and $p_{T}(jet)>$10 GeV/c in p+p collisions at $\sqrt{s}$ = 500 GeV by the STAR experiment. The comparison to model calculations and similar measurements carried out at the LHC will be presented, and its physics implications will be discussed.
We study inclusive $J/\psi$ photoproduction at NLO at large $P_T$ at HERA and the EIC. Our computation includes NLO QCD leading P_T corrections, QED contributions via an off-shell photon as well as those from $J/\psi$+charm channels. For the latter, we employ the variable-flavour-number scheme. Our results are found to agree with the latest HERA data by H1 and provide, for the first time, a reliable estimate of the EIC reach for such a measurement. Finally, we demonstrate the observability of $J/\psi$+charm production and the sensitivy to probe the non-perturbative charm content of the proton at high $x$, also known as intrinsic charm, at the EIC.
Recent results from the ATLAS experiment on charmonium production will be presented. The measurement of the associated production of the J/psi meson and a photon, including an estimation of the transverse-momentum-dependent distribution function of linearly polarized gluons in an unpolarized proton, will be discussed. The measurement of J/psi and psi(2S) differential cross sections at large and medium transverse momentum values will be also reported.
Transverse momentum dependent parton distribution functions (TMDs) are extensions of the well- known collinear PDFs. They contain, apart from the usual x- and scale dependence, also information on the intrinsic transverse momentum carried by the parton, and on the spin correlations.
Experimentally, not so much is known about gluon TMDs, since they are subleading with respect to their quark counterparts in the few processes for which TMD factorization is proven (Drell-Yan, SIDIS). This problem is bypassed by studying quarkonium, to which the gluon distributions in the proton couple already at leading order.
In this seminar, I will review two recent studies [1,2] where inclusive and associated quarkonium electroproduction is put forward as a probe of the proton gluon TMDs. I will then elaborate on subtleties [3] that arise, related to the transverse-momentum dependence of the so-called long distance matrix elements (LDMEs), which encode the nonperturbative information on the hadronization of the heavy-quark pair.
[1] A. Bacchetta, D. Boer, C. Pisano, and P. Taels, Gluon TMDs and NRQCD matrix elements in production at an EIC, Eur. Phys. J. C 80 (2020) 72
[2] U. D’Alesio, F. Murgia, C. Pisano, and P. Taels, Azimuthal asymmetries in semi-inclusive J/ψ+jet production at an EIC, Phys. Rev. D 100 (2019) 094016
[3] D. Boer, U. D’Alesio, F. Murgia, C. Pisano, and P. Taels, J/ψ meson production in SIDIS: matching high and low transverse momentum, JHEP 09 (2020) 40
The Belle II experiment at the SuperKEKB energy-asymmetric $e^+ e^-$ collider is an upgrade of the B factory facility at KEK in Tsukuba, Japan. The experiment began operation in 2019 and aims to record a factor of 50 times more data than its predecessor. 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. We present recent results in new Belle II data, and the future prospects to explore both exotic and conventional quarkonium physics.
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 paper, 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 Phys.Rev.D 101 (2020) 3, 034030.
LHCb is a fully instrumented spectrometer covering the forward rapidity region at the LHC, and provides unique access to the small x region inside the nucleus. This talk will present a selection of recent results from the LHCb heavy ion program, including data on charged hadrons, open charm and charmonia production in pPb collisions, and J/psi production in peripheral PbPb collisions. Comparisons with calculations and effects from the nuclear PDF and dense QCD medium will be discussed.
In this talk we present the analysis of prompt photon production at the LHC with the kT-factorization approach. We consider two leading partonic channels, qg->q\gamma and gg*->q\bar{q}\gamma and three theoretical schemes known under the acronyms KMR, GBW, CCFM. We find sensitivity of the calculated prompt photon transverse momentum distribution to the gluon transverse momentum distribution. The predictions are compared to precise data from ATLAS and CMS experiments, what allows to differentiate between approaches.
We present, the results of a phenomenology analysis at Next-to-Leading accuracy for the Mueller-Tang jet process, where two jets separated by a large rapidity interval and no other radiation are observed. This process is of high interest, as one might be able to investigate Balitsky-Fadin-Kuraev-Lipatov (BFKL) dynamics which emerges in the high-energy limit of quantum chromodynamics (QCD).
Two are the key ingredients in the BFKL framework. The Gluon-Green 4-point function (GGF) a, process independent, universal object that is exchanged in the collision and the Impact-Factors (IF) which couple the GGF with the external probes.
The novelty in this study consists in including in the analysis also the NLO corrections of the IFs. Aside from the expected complications due to the NLO IF enriched topology, a more puzzling problem emerged during this study. The precise observable definition enforced also at experimental level preclude a construction featuring the high-energy factorization, namely the separation of IF and GGF so that all the BFKL resummed enhancing factors can be cast into the GGF alone.
On the experimental side, fair agreement has been found between BFKL predictions and Tevatron data. The CMS experiment has presented results at collision energies of 7 and 13 TeV. However, no clear-cut evidence of the BFKL dynamics can be claimed yet. To confirm and distinguish the role of the underling BFKL dynamics a complete analysis at NLO is needed. In this talk, we present progress toward such a task. We recall some of the difficulties encountered along the way, with emphasis on the mentioned breaking of the high-energy factorization and compare the predictions to the CMS findings at 13 TeV.
This paper presents an experimental study of proton-proton collision events where the two leading jets are separated by a large pseudorapidity interval devoid of particle activity, referred to as jet-gap-jet events. The pseudorapidity gap is expected from hard color-singlet exchange. The analysis is based on data collected by the CMS and TOTEM experiments during a low luminosity, high-$\beta^*$ run at the CERN LHC in 2015. Events with a low number of charged particles between the jets are observed in excess of calculations that assume only color-exchange dijet contributions. The fraction of dijet events produced via color-singlet exchange, $f_\text{CSE}$, is measured as a function of $p_\text{T}^\text{jet2}$, the pseudorapidity difference between the two leading jets, and the azimuthal angular separation between the two leading jets. The fraction $f_\text{CSE}$ has values of $0.6$--$1.0$\%. It increases with the pseudorapidity difference between the jets, has a weak dependence on $p_\text{T}^\text{jet2}$, and increases as the azimuthal angular difference between the jets approaches $\pi$. The results are compared with previous measurements and with predictions from perturbative quantum chromodynamics. In addition, the paper presents the first study of jet-gap-jet events detected in association with an intact proton, interpreted as a proton-gap-jet-gap-jet topology, using a subsample of events with an integrated luminosity of $0.40\,\text{pb}^{-1}$. The intact protons are detected with the Roman pot detectors of the TOTEM experiment. The $f_\text{CSE}$ measured in this sample is $2.91 \pm 0.70$ (stat) $^{+ 1.02}_{- 0.94}$ (syst) times larger than that for inclusive dijet production in dijets with similar kinematics.
Inclusive measurements of forward back-to-back dijets/dihadrons in deeply inelastic scattering (DIS) present a promising channel to access signatures of gluon saturation inside nuclear matter at the future Electron-Ion Collider (EIC). Most phenomenological studies employ the transverse momentum dependent (TMD) factorization framework; however, there are important kinematic (perturbative power) and genuine saturation corrections that must be resummed for more controlled phenomenological predictions. The Color Glass Condensate (CGC) is a suitable framework that resums both types of contributions in the small-x regime.
In this talk, I will present our novel results for inclusive diparton production in proton and nuclear DIS from full multi-gluon correlations in the CGC using the Gaussian approximation of high energy correlators and the Balitsky-Kovchegov evolution with running coupling. We compare our numerical results to the TMD framework for a wide range of kinematics accessible at the future EIC. We find that both kinematic and genuine saturation corrections are significant and could be accessed in measurements of azimuthal correlations of dijets and dihadrons.
This talk is based on [1,2].
[1] H. Mäntysaari, N. Mueller, F. Salazar, B. Schenke. Multi-gluon correlations and evidence of saturation from dijet measurements at an Electron-Ion Collider. Phys. Rev. Lett. 124, 112301 (2020)
[2] R. Boussarie, H. Mäntysaari, F. Salazar, B. Schenke. Work in preparation.
We study production of two jets in DIS for EIC kinematics using the small-x improved TMD factoriztion (ITMD) framework. The ITMD can be derived within the Color Glass Condensate (CGC) as an adequate limit when the hard scale is considerably higher than the saturation scale, but being still in the nonlinear domain. Production of two tagged colored partons in photon-nucleus collisions is the basic process directly coupled to the Weizsacker-Williams (WW) transverse momentum dependent (TMD) gluon distribution. Unlike the dipole TMD gluon distribution, which couples to inclusive DIS, the WW TMD distribution possesses the gluon number interpretation and is known to behave drastically different in the small kT regime. We study various observables potentially sensitive to interplay of the Sudakov effects and the nonlinear effects, in particular the azimuthal correlations between the jets, as well as the correlations between the jet system and the scattered electron. Our calculations are based on the WW TMD gluon distribution calculated from the dipole TMD distribution fitted to HERA data, in the mean field CGC approaximation and with the inclusion of the pertubative Sudakov factor.
A framework to study gluon saturation in QCD using trijet processes is presented.
The so-called small-x Improved Transverse Momentum Dependent factorization (ITMD) was originally formulated for the dijet final states in hadron collisions. I present results for a multiparton extension, in particular for trijets both for proton-proton and proton-lead collisions at center of mass energy 5.02 TeV. Differences related to both the change from standard kT-factorization to ITMD factorization as well as differences between p-p collision and p-Pb are shown. Large changes in the distributions going from one to the other factorization approach allow to improve the small-x gluon distributions and to validate the two approaches. The significant reduction of the nuclear modification ratio indicates that it may be possible to use trijets in the search for saturation effects.
We present recent results of transverse single-spin asymmetries (TSSA) for neutral pions using the Forward Meson Spectrometer at STAR at center of mass energies of 200 and 500 GeV in proton-proton collisions. The results from the two energies show that the pion TSSA increases continuously with Feynman-x. Comparisons with previous measurements show that the pion TSSA is mostly independent of collision energy from 20 GeV to 510 GeV. It is found that isolated pions with no other particles nearby tend to have higher TSSA than the non-isolated ones which may suggest different mechanisms for the TSSA. In order to separate the contributions of initial and final state effects at both energies, we also measure the TSSA 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 dependence of the pion TSSA, but with a significantly smaller amplitude. The Collins asymmetry is consistent with zero and shows evidence of a jT dependence, which is the pion transverse momentum with respect to the jet axis. These results provide rich information to understand the physics mechanism of TSSA in hadron collisions.
The experimental observation of strikingly large transverse single-spin asymmetries (TSSAs) revealed that there were significant spin-momentum correlations present in hadronic collisions, both within nucleons and the process of hadronization. TSSA measurements have allowed for the development of both transverse momentum dependent and collinear twist-3 descriptions of these nonperturbative spin-momentum correlations. Results are presented for the TSSAs of direct photons, neutral pions, and eta mesons for $|\eta|<0.35$ from $p^\uparrow + p$ collisions with $\sqrt{s} = 200$ GeV at PHENIX. As hadrons, $\pi^0$ and $\eta$ mesons are sensitive to both initial- and final-state effects and at midrapidity probe the dynamics of gluons along with a mix of quark flavors. Because direct photon production does not include hadronization, the direct photon TSSA is only sensitive to initial-state effects and at midrapidity provides a clean probe of the gluon dynamics in transversely polarized protons. All three of these results will help constrain the collinear twist-3 trigluon correlation function as well as the gluon Sivers function, improving our knowledge of spin-dependent gluon dynamics in QCD.
Understanding the transverse spin and momentum structure of the proton is of large interest to the nuclear physics community and it is one of the main goals of the spin physics program at the Relativistic Heavy Ion Collider (RHIC). Transverse single spin asymmetry measurements for charged particles produced in proton proton collisions provide keen insight into initial and final state spin-momentum and spin-spin correlations of partons within hadrons. In particular, electrons from heavy flavor decays provide access to initial state spin-momentum correlations of gluons in the proton, while charged pions provide access to both initial and final state transverse spin effects of quarks and gluons. Electrons and charged pions are measured at midrapidity at PHENIX using the central arm spectrometers which consist of an Electro-Magnetic Calorimeter, a Ring-imaging Cherenkov Detector, as well as Drift and Pad Chambers. In addition, the heavy flavor decay electron analysis uses the Silicon Vertex Detector (SVX) in order to veto background from conversion electrons. The status of both the electron and charged pion measurements from the 2015 running period (200 GeV $p+p^{\uparrow}$) will be presented including the recent result for the transverse single spin asymmetry of electrons from open heavy flavor decays.
Proton at high energy is a hugely complex many-body quantum system where gluons are the dominant degrees of freedom. The information of the three-dimensional structure of the proton is encoded in the transverse Momentum Dependent Parton distribution function (TMDs). Transverse Momentum Dependent Parton distribution functions (TMDs) are among the key subjects to be fully investigated at current and future Electron-Ion Collider (EIC) facilities including JLabs 12 GeV Upgrade, eRHIC and the planned EIC. A lot of work has been done for the extraction of quark TMDs but relatively very little is known about the gluon TMDs. Quarkonium production processes provide good opportunities to study gluon TMDs. There are three models that have been used to study the production mechanism of quarkonium: The color octet, color singlet, and color evaporation model.
Here we are calculating the $cos2\phi$ asymmetry in $J/\psi$ production in an unpolarised electron-proton collision using the NRQCD based color octet model within the kinematical range of the planned Electron-Ion Collider (EIC). This can directly probe the linearly polarized gluon distribution in the unpolarized proton. The asymmetry is calculated within the kinematical region $z<1$, where the NLO subprocess $\gamma*+g\rightarrow J/\psi+g$ gives the leading contribution. We calculated the upper bound of the asymmetry as well as estimate it using a Gaussian-type parametrization for the transverse momentum dependent Parton distributions and McLerran-Venugopalan model at small $x$. We present the numerical results.
We study the Sivers azimuthal asymmetry, and the role of the gluon Sivers function (GSF), in inelastic $J/\psi$ leptoproduction, $l\,p^\uparrow \to l'+ J/\psi+ X$, at small-to-moderate transverse momentum. To this end, we adopt the color-gauge invariant generalized parton model and the NRQCD framework for quarkonium formation. We compare our estimates for the unpolarized cross-section with available data from ZEUS and H1. We also compare the Sivers asymmetry obtained by maximizing the GSF with the available data point from COMPASS. Finally, we present estimates for the maximized Sivers asymmetry at the EIC energy.
Using Soft-Collinear Effective Theory, we develop the transverse-momentum-dependent factorization formalism for heavy flavor dijet production in polarized-proton-electron collisions. We consider heavy flavor mass corrections in the collinear-soft and jet functions, as well as the associated evolution equations. Using this formalism, we generate a prediction for the gluon Sivers asymmetry for charm and bottom dijet production at the future Electron-Ion Collider. Furthermore, we compare theoretical predictions with and without the inclusion of finite quark masses. We find that the heavy flavor mass effects can give sizable corrections to the predicted asymmetry.
We show that jet charge measurements can substantially enhance the sensitivity of spin asymmetries to different partonic flavors in the nucleon. As an example, we
use the Sivers asymmetry in back-to-back electron-jet production at the EIC to show that the jet charge can be a unique tool in constraining the Sivers function for different partonic flavors.
I review recent developments in the global QCD analysis by the CTEQ-TEA group that follows the public release of the new CT18 NNLO parton distributions last year [arXiv:1912.10053]. The role of LHC experiments at 7, 8, and 13 TeV in constraining the CT PDFs is discussed. Theoretical and methodological advancements aimed at obtaining reliable central PDFs and their uncertainties are reviewed, including NNLO corrections, advanced parametrization forms, small-x saturation scale, alternative tolerance definitions.
We present recent updates from the CTEQ-Jefferson Lab (CJ) global analysis of parton distribution functions with a new set of electroweak measurements. Electroweak measurements in proton collisions provide unique access to quark flavor separation and strangeness in the proton. In particular, recent W and Z boson measurements from the STAR experiment at RHIC are included which provide additional constraint to the light sea quarks near the valence regime while the LHC data probe smaller x region. In this talk, the impact of the new data sets on parton distribution functions will be presented with a emphasis given to the flavor asymmetry of the light quark sea at large-x region.
We present a new release of the NNPDF family of global analyses of parton distribution functions: NNPDF4.0. It includes a wealth of new experimental data from HERA and the LHC, from dijet cross-sections to single-top and top-quark pair differential distributions. The NNPDF4.0 methodology benefits from improved machine learning algorithms, in particular automated hyperparameter optimisation and stochastic gradient descent for neural network training, which has been validated extensively by means of closure tests and future tests. We demonstrate the stability of the result with respect to the choice of parameterisation basis. We compare NNPDF4.0 with its predecessor NNPDF3.1 as well as to other recent global fits, and study its phenomenological implications for representative collider observables. We assess the impact of representative datasets on specific PDF combinations, such as the dijet and top quark data on the gluon, the Drell-Yan and neutrino DIS data on strangeness, and electroweak measurements on charm and quark flavour separation.
Recent developments of the xFitter PDF analysis package and studies based on it are summarised. The emphasis is given to the PDF analysis of the Z boson polarisation data which provide additional constraint to the gluon distribution for Bjorken x below 0.1. Studies using pseudo data samples corresponding to an integrated luminosity of the LHC Run 3 and high-luminosity HL-LHC show that the PDF uncertainty of the Higgs boson production cross section can be reduced significantly.
We present the new MSHT2020 set of parton distribution functions (PDFs) of the proton, determined from global analyses of the available hard scattering data. The PDFs are obtained using the same basic framework as MMHT2014, but supersede these. The parameterisation is now adapted and extended and we include a large number of new data sets: from the final HERA combined data on total and heavy flavour structure functions, to final Tevatron data, and in particular a significant number of new LHC 7 and 8 TeV data sets on vector boson production, inclusive jets and top quark distributions. We include up to NNLO QCD corrections for all data sets that play a major role in the fit, and NLO EW corrections where relevant. There are some changes to central values and a significant reduction in the uncertainties of the PDFs in many cases, but the PDFs and the resulting predictions are generally within one standard deviation of the MMHT14 results. The major changes arevalence quark difference, the anti-up anti-down difference at small x, and the strange quark PDF We discuss the phenomenological impact of our results, e.g. predictions for processes such as Higgs, top quark pair and vector bosonproduction. We briefly discuss the
variation of PDFs and the fit with changes in the strong coupling and heavy quark masses.
At large values of $x$ the parton distribution functions (PDFs) of the proton are poorly constrained and there are considerable variations between different global fits. Data at such high $x$ have already been published by the ZEUS Collaboration, but not yet used in PDF extractions. A technique for comparing predictions based on different PDF sets to the observed number of events in the ZEUS data 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 universality of the couplings of the different generations of leptons to the electroweak gauge bosons is at the core of the Standard Model of particle physics. In this contribution, a measurement of the ratio of the rate of decay of W bosons to τ-leptons and muons, R(τ/μ)=B(W→τντ)/B(W→μνμ), is presented, that constitutes an important test of this axiom. The measurement is based on a novel technique that takes advantage of the abundant W-boson sample produced in top quark decay, in 139 fb−1 of data recorded with the ATLAS detector in proton--proton collisions at sqrt(s)=13 TeV. The value of R(τ/μ) is found to be 0.992±0.013, in agreement with the hypothesis of universal lepton couplings as postulated in the Standard Model. This is the most precise measurement of this ratio, and the only such measurement from the Large Hadron Collider, to date.
Measurements of the differential cross sections of Z + jets and γ + jets production, and their ratio, are presented as a function of the boson transverse momentum. Measure- ments are also presented of the angular distribution between the Z boson direction and a jet in events where the Z boson is emitted collinear with a jet. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC. The data are compared with various theoretical predictions after correcting for the detector effects. In general, the predictions at higher orders in perturbation theory show better agreement with the data. These results represent the first measurement of the differential cross section ratio of Z + jets and γ + jets production at 13 TeV and the first explicit measurement of collinear Z emission.
The description of the Drell-Yan (DY) transverse momentum spectrum requires matching of fixed order QCD calculations with soft gluon resummation up to all orders in the QCD coupling. It has been noticed in the literature that a consistent description of DY data in a wide kinematic regime from fixed-target to LHC energies is problematic. In this talk the predictions for transverse momentum spectrum of DY data coming from experiments in very different kinematic ranges (NuSea, R209, Phenix, LHC 8 TeV and 13 TeV center-of-mass energies $\sqrt{s}$) are calculated by applying transverse momentum dependent (TMD) parton distributions obtained from the Parton Branching (PB) method, combined with the next-to-leading-order (NLO) calculation of the hard process in the MCatNLO method. We discuss the problems involved in matching of the fixed order calculation and resummation, especially in the moderate to low mass and pT region accessible at fixed target experiments. We find that at low DY mass and low $\sqrt{s}$ 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.
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 various center-of-mass energies. Measurements of the transverse momentum distribution of the vector boson at 13 TeV are also presented. The measurements are corrected for detector inefficiency and resolution and compared with state-of-the-art theoretical calculations.
Thanks to the large amount of data that is being and will be collected at Run-III and High Luminosity (HL) stage, precision measurements at the LHC are reaching an unprecedented level of statistical accuracy, whilst PDF uncertainties prevail. We study the impact of future measurements of lepton-charge and forward-backward asymmetries on PDF determination. The numerical results have been obtained employing the open-source platform xFitter and standard profiling procedures. We explore the potential of the combination of charged-current and neutral-current Drell-Yan (DY) asymmetries in regions of transverse and invariant masses near the SM gauge bosons peaks to improve the PDF uncertainties.
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.
The STAR forward upgrade consisting of new tracking and electromagnetic and hadronic calorimeter systems covering a pseudorapidity range of 2.5-4.5 will start data taking in autumn 2021. A core motivation is the exploration of the structure of nuclei at very high and low regions of Bjorken x. The forward upgrade also provides new detector capabilities at RHIC and STAR to explore the longitudinal structure of the initial state and the temperature dependent transport properties of matter in relativistic heavy ion collisions. This talk gives an overview of the STAR forward upgrade physics program along with the current status of the different detector subsystems.
Jet production and jet substructure in reactions with nuclei at future electron ion colliders will play a preeminent role in the exploration of nuclear structure and the evolution of parton showers in strongly-interacting matter. In the framework of soft-collinear effective theory, generalized to include in-medium interactions, we present the first theoretical study of inclusive jet cross sections and the jet charge at the EIC. Predictions for the modification of these observables in electron-gold relative to electron-proton collisions reveal how the flexible center-of-mass energies and kinematic coverage at this new facility can be used to enhance the signal and maximize the impact of the electron-nucleus program. Importantly, we demonstrate theoretically how to disentangle the effects from nuclear parton distribution functions and the ones that arise from strong final-state interactions between the jet and the nuclear medium.
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 [1]. 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.
[1] LHeC Collaboration and FCC-he Study Group, P. Agostini et al., e-Print: 2007.14491 [hep-ex].
The recent exclusive backward-angle electroproduction of omega from Jefferson Lab Hall C electron-proton fixed-target scattering experiments above the resonance region, published in the PRL, hints on a new domain of applicability of QCD factorization in a unique u-channel kinematics regime. Thanks this pioneering effort, the interests of studying nucleon structure through u-channel meson production observables have grown significantly.
In the fixed target configuration, the u-channel meson electroproduction observables feature an unique interaction picture: target proton absorbs nearly all momentum induced by virtual photons and recoils forward; while the production mesons (such as omega or pions) are left behind almost at rest near the target station. At Jefferson Lab Hall C, the missing mass reconstruction technique is applied to resolve the produced nucleon; whereas in Hall B and D, the decayed mesons are directly detected. In this presentation, I will provide a summary on the key observations of the existing u-channel meson production results, update-to-date theory insights and a path to further explore u-channel observables from JLab 12 GeV Hall C program to the future Electron Ion Collider.
Nuclear dynamics at short distances among nucleons is one of the most outstanding phenomena in nuclear physics. Understanding the role of QCD in generating nuclear forces is important for uncovering the underlying physics of Short-Range Correlations (SRCs). In recent years, SRCs has 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 with collider experiments, e.g., the Electron-Ion Collider (EIC). The experimental technique of studying the light nuclei can be based on exclusive processes with tagging final-state particles, in order to fully control the initial state of the target wavefunction. In particular, incoherent diffractive production of $J/\psi$ particle off deuteron will be presented. In addition, the spectral function in light nuclei has been recently modeled in the BeAGLE event generator, where the decay kinematics of the light nuclei and their influence on the very forward detector design at the EIC will be discussed.
Recent results from the ATLAS experiment on exotic heavy hadrons will be presented. Studies of the Pentaquarks with hidden charm in the Lambda_b decays in proton-proton collisions at 7 - 8 TeV will be discussed. New results on the heavy tetraquarks in the Run 2 data at 13 TeV will also be reported.
We discuss the production mechanism of a new state, a fully charm tetraquark, discovered recently by the LHCb at M = 6.9 GeV in the $J/\psi J/\psi$ channel. Both single parton scattering (SPS) and double parton scattering (DPS) mechanisms are considered. We calculate the distribution in the invariant mass of the four-quark system $M_{4c}$ for SPS and DPS production of $c c \bar c \bar c$-system in the $k_T$-factorization approach with modern unintegrated gluon distribution functions (UGDFs). The so-calculated contribution of DPS is almost two orders of magnitude larger than the SPS one, but the tetraquark formation mechanism is unknown at present. We construct a simple coalescence model of the tetraquark out of $c \bar c c \bar c$ continuum. Imposing a mass window around the resonance position we calculate the corresponding distribution in $p_{T,4c}$ - the potential tetraquark transverse momentum. The cross section for the $J/\psi J/\psi$ continuum is calculated in addition, again including SPS (box diagrams) and DPS contributions which are of similar size. The formation probability is estimated trying to reproduce the LHCb signal-to-background ratio. The calculation of the SPS $g g \to T_{4c}(6900)$ fusion mechanism is performed in the $k_T$-factorization approach assuming different spin scenarios ($0^+$,$0^-$ and $2^+$). The $2^+$ and $0^+$ assignment is preferred over the $0^-$ one by the comparison of the transverse momentum distribution of signal and background with the LHCb preliminary data assuming the SPS mechanism dominance. There is no microscopic approach for the DPS formation mechanism of tetraquarks at present as this is a complicated multi-body problem. We do similar analysis for FCC energy $\sqrt{s}$ = 100 TeV. We predict cross section order of magnitude larger than its counterpart for the LHC. We discuss also a possibility to observe the $T_{4c}$ state in the $\gamma \gamma$ channel. The signal-to-background ratio is estimated.
First part of the presentation will be based on our recent paper:
R. Maciula, W. Schafer and A. Szczurek, "On the mechanism of $T_{4c}(6900)$ tetraquark production", Phys. Lett. B812 (2021) 136010.
Exotic hadrons, which are composed of more than three valence quarks, can provide new insights into the internal structure and dynamics of hadrons, thus improving our knowledge of the non-perturbative regime of QCD. The data collected by the LHCb experiment provides unique opportunities for precise measurement of properties of established exotic hadrons and search for new ones. This talk discusses the recent results of exotic hadron studies at LHCb.
In this talk, we present a thorough analysis of $\eta_c(1S, 2S)$ and $\chi_{c0},\chi_{b0}$ quarkonia hadroproduction in $k_T$-factorisation in the framework of the light-front potential approach for the quarkonium wave function.
The off-shell matrix elements for the $g^{*}g^{*}\to\eta_c, \chi_{c0}$
vertices are derived in terms of the quarkonium light-front wave function.
We discuss the role of the Melosh spin-rotation and relativistic corrections estimated by comparing our results with those in the standard nonrelativistic QCD (NRQCD) approach. We elaborate on the importance of taking into account the gluon virtualities, which distinguishes our approach from the ones based on TMD distributions.
We compare our results for $\eta_c (1S)$ to measurements by the LHCb collaboration. The LHCb kinematics probes one of the gluons at small-$x$, and we
consider the possible impact of gluon saturation effects.
Based on:
I.Babiarz, R.Pasechnik, W.Schafer and A.Szczurek,
``Prompt hadroproduction of $\eta_c(1S,2S)$ in the $k_T$-factorization approach,''
JHEP 02, 037 (2020)
doi:10.1007/JHEP02(2020)037
[arXiv:1911.03403 [hep-ph]].
I.Babiarz, R.Pasechnik, W.Schafer and A.Szczurek,
``Hadroproduction of scalar $P$-wave quarkonia in the light-front k$_{T}$ -factorization approach,''
JHEP 06, 101 (2020)
doi:10.1007/JHEP06(2020)101
[arXiv:2002.09352 [hep-ph]].
The large data sample accumulated by the Belle experiment at the KEKB asymmetric-energy e^{+}e^{-} collider provides a unique opportunity to perform studies related to hadron spectroscopy utilising various production mechanisms. We report on radiative decays of excited Xi_c baryons, study of Xi_c → Xi_0 K+ K0, branching fraction measurement of Lambda_c^+, determination of the spin and parity of charmed strange meson Xi_c(2970)+. We also cover recent study on charmonia, e.g. X(3872) in two-photon productions and search for resonant states with ccbarssbar quark content, and bottomonia.
Heavy quarkonium production provides valuable opportunities for exploring 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 in terms of expansion in powers of $\alpha_s$ and the relative velocity of the heavy quark pair does not include the full resummation of powers of $\ln(p_T^2/m_Q^2)$ for high $p_T$ quarkonium production. In previous studies [1,2,3], a QCD factorization formula for high $p_T$ quarkonium production was derived up to next-to-leading power 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 functions for quarkonium production, which effectively resums the power of $\ln(p_T^2/m_Q^2)$-type contributions [4]. In particular, we will discuss how to simplify the complicated nonlinear evolution equations [1] and emphasize the importance of input distribution functions [5,6] in $z$ space. We demonstrate how the $p_T$ distribution of unpolarized quarkonium production cross section is modified when taking the quantum evolution into account. We also discuss the impact of the quantum evolution on 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 and G. Sterman, JHEP 09, 046 (2020).
[4] K. Lee, J. W. Qiu, G. Sterman, and K. Watanabe, in preparation.
[5] Y. Q. Ma, J. W. Qiu, and H. Zhang, Phys. Rev. D 89, no. 9, 094029 (2014).
[6] Y. Q. Ma, J. W. Qiu, and H. Zhang, Phys. Rev. D 89, no. 9, 094030 (2014).
One of the key components to solving the proton spin problem is understanding the small-x asymptotics of the helicity parton distribution functions (hPDFs). Several years ago, novel, small-x evolution equations were derived using the shock-wave/Wilson line formalism, designed for calculating the x-dependence of the quark and gluon hPDFs and the proton g1 structure function. These equations can be used to predict the contribution to the spin of the proton coming from the helicities of the small-x quarks and gluons. In this talk we will present the first-ever attempt to describe the world data on the g1 structure function at small x using the evolution equations derived the novel evolution equations within the JAM global analysis framework. Our results serve as a prediction for future measurements at the EIC and can be used to estimate the net amount of quark spin at small-x, ultimately bringing us one step closer to understanding the proton spin.
*This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Award Number DE-SC0004286.
We apply the formalism developed earlier $[1,2]$ for studying the small-$x$ asymptotics of transverse momentum dependent parton distribution functions (TMDs) to construct the small-$x$ asymptotics of the quark Sivers function. We explicitly construct the transversely polarized, fundamental "Wilson line" operator to sub-sub-eikonal order. We then express the Sivers function in terms of dipole scattering amplitudes containing the transversely polarized "Wilson line", and show that the main term which contributes to the Sivers function is the spin-dependent odderon, similar to the case of the gluon Sivers function derived by Boer, Eschevarria, Mulders and Zhou [3] (see also [4]).
[1] Y. V. Kovchegov and M. D. Sievert, Phys. Rev. D99, 054032 (2019).
[2] Y. V. Kovchegov and M. D. Sievert, Phys. Rev. D99, 054033 (2019).
[3] D. Boer, M. G. Echevarria, P. Mulders, and J. Zhou, Phys. Rev. Lett. 116, 122001 (2016).
[4] L. Szymanowski and J. Zhou, Phys. Lett. B760, 249 (2016).
Within the Color Glass Condensate effective theory or other related frameworks, the theoretical description of low-x (or high-energy) QCD processes sensitive to the nonlinear gluon saturation physics relies on two main pillars.
The first one is the semiclassical approach: due to the high density of low x gluons in an incoming proton or nucleus target, scattering processes off that target reduce to scattering processes on a semiclassical background gluon field. In particular, dense-dilute scattering processes at low x can then be formulated within perturbation theory in presence of a strong background gluon field.
The second main pillar is the eikonal approximation, which amounts to neglecting power-suppressed corrections in the high-energy limit. Within the semiclassical framework, the eikonal approximation is equivalent to an infinite Lorentz boost of the background field, which is then contracted to a gluon shockwave. This approximation is crucial to make possible the systematic resummation of multiple interactions with the target. It is by definition a better and better approximation as the energy of the collision increases. But corrections beyond the eikonal approximation can be large at intermediate energies, in particular at RHIC and EIC, and their study is thus becoming a priority.
In this talk, I will present the calculation of the complete next-to-eikonal corrections (first subleading power) to the quark propagator through the target, including both the effects of the finite longitudinal width of the target and of the transverse components of the background field. It extends our previous results on the gluon propagator, which included finite target width corrections only. I will also present the first applications of this next-to-eikonal quark propagator to the calculation of next-to-eikonal corrections to a few selected observables in pA collisions or DIS.
We calculate the inclusive quark-photon production in high energy proton-nucleus collisions using a new formalism which includes the dynamics of gluon saturation at small $x$ as well as large x gluons of the target. We show how this unified formalism can be applied to di-jet production in DIS at all Bjorken x.
Quasi parton distribution functions (PDFs) are related to the matrix elements of bilocal operators with space-like separation. The possibility to calculate these objects on the lattice has attracted much attention in the QCD community. I will present the behavior of quark and gluon quasi-PDFs at low-x.
Understanding the relation between QCD evolution in the Bjorken limit and the Regge limit is crucial to achieve a complete and smooth picture of proton and nuclear structure. The hope in the small x regime (where gluon density is expected to reach saturation and the naif partonic breaks down), was that by computing higher order corrections to small x evolution (BK equations) one would capture more and more of the physics at moderate x. However, this research program has encountered some challenges. At NLO large collinear logarithms are present and need to be resummed spoiling the renormalization group structure established at LO.
In order to overcome these formal difficulties, we revisit the shock wave approach for high energy scattering. A new gauge invariant operator definition of the unintegrated gluon distribution that accounts systematically for the collinear limit of structure functions emerges naturally in our framework. I will discuss in particular inclusive DIS as a first application.
A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published \hermes results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing $\cos{\phi-\phi_s}$ modulations provide evidence for a sizable worm-gear (II) distribution, $g_{1T}$. Most of the other modulations are found to be consistent with zero with the notable exception of large $\sin{\phi_s}$ modulations for charged pions and $K^+$.
The exploration of the transverse spin structure of the nucleon by measuring the transverse-spin-dependent azimuthal asymmetries in Drell-Yan process is one of the main topics of the phase-II research programme of the COMPASS experiment (CERN, SPS-M2 beamline).
In 2015 and 2018 the experiment performed Drell-Yan measurements using a 190 GeV $\pi^-$ beam interacting with a transversely polarized $NH_3$ target and unpolarized tungsten material. The angular coefficients \lambda, \mu and \nu that describe the unpolarized part of the Drell-Yan cross section have been extracted from the data collected with tungsten target. Obtained results provide important information to study various perturbative and non-perturbative QCD effects. Performed polarized measurements of the Sivers and other transverse azimuthal asymmetries in Drell-Yan provide a unique possibility to test predicted in QCD (pseudo-)universal features of related transverse momentum dependent parton distribution functions.
In this talk recent preliminary results from the COMPASS Drell-Yan programme will be presented together with related measurements from other experiments and available model predictions.
We perform the global analysis of polarized Semi-Inclusive Deep Inelastic Scattering (SIDIS), pion-induced polarized Drell-Yan (DY), and W/Z boson production data and extract the Sivers function for u, d, s and for sea-quarks. We use the framework of transverse momentum dependent factorization at N3LO accuracy. The Qiu-Sterman function is determined in a model-independent way from the extracted Sivers function. We also evaluate the significance of the predicted sign change of Sivers function in DY with respect to SIDIS
The Bayesian reweighting procedure is applied for the first time to a transverse momentum dependent distribution, the quark Sivers function extracted from Semi-Inclusive DIS (SIDIS) data. By exploting the recent published single spin asymmetry data for the inclusive jet production in $p^\uparrow p$ collisions from the STAR collaboration at RHIC, we show how such a procedure allows to incorporate the information contained in the new data set, without the need of re-fitting, and to explore a much wider $x$ region compared to SIDIS measurements. The reweighting method is also extended to the case of asymmetric errors, and the results show a significant improvement of the knowledge of the quark Sivers function.
Pseudo-data with simulated experimental errors can be generated to train an ensemble of Artificial Neural Networks (ANN) implemented on a regression to extract Transverse Momentum-dependent Distributions (TMDs). A preliminary analysis will be presented on the reliability in extraction of the Sivers function imposed in the pseudo-data given the bounds on the experimental errors, data sparsity, and complexity of phase-space.
We perform explorative analyses of the 3D gluon content of the proton via a study of unpolarized and polarized gluon TMDs at twist-2, calculated in a spectator model for the parent nucleon. Our approach embodies a flexible parametrization for the spectator-mass function, suited to describe both moderate and small-$x$ effects. All these studies can serve as a useful guidance in the investigation of the gluon dynamics inside nucleons and nuclei, which constitutes one of the major goals of new-generation colliding machines, as the EIC, the HL-LHC and NICA.
We present a new global QCD analysis of inclusive DIS data, using a Monte Carlo approach to extract the spin-averaged 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 important. We focus in particular on the quantification of the nuclear corrections, including Fermi motion, binding and nucleon off-shell effects, in the deuterium nucleus. We quantify the effects on the extracted PDFs and the nuclear corrections from various theoretical treatments of the power corrections and nuclear wave functions.
As data become more precise, estimating theoretical uncertainties in global PDF determinations is likely to become increasingly necessary to obtain correspondingly precise PDFs. Here we present a next generation of global proton PDFs (NNPDF4.0) that include theoretical uncertainties due to the use of heavy nuclear and deuteron data in the fit. We estimate these uncertainties by comparing
the values of the nuclear observables computed with the nuclear PDFs against those computed with proton PDFs. For heavy nuclear PDFs we use the nuclear nNNPDF2.0 set, while for deuteron PDFs we develop an iterative procedure to determine proton and deuteron PDFs simultaneously, each including the uncertainties in the other. Accounting for nuclear uncertainties resolves some of the tensions in the global fit of the proton PDFs, especially those between the nuclear data and the extended LHC data set used in NNPDF4.0.
Parton distribution functions (PDFs) for quarks and gluons inside the proton are needed for predicting a variety of processes at the LHC, including Higgs boson production and searches for new physics beyond the Standard Model. PDF parametrizations are obtained by fitting a large number of cross-sections from many experiments at different (x,Q^2). In the global analyses of PDFs by CTEQ collaboration, we find that deeply inelastic scattering experiments on nuclear targets provide important constraints on combinations of PDFs relevant to the LHC electroweak precision measurements. What is the role of these experiments in the LHC era, and how influenced are they by nuclear effects? I explore this complex question using a new statistical indicator called "PDF sensitivity" for analyzing the impact and compatibility of experiments in a PDF fit.
We report on our progress in updating our global analysis of nuclear PDFs. In particular, we will discuss the inclusion of double differential 5TeV dijet and D-meson measurements, as well as 8TeV electroweak data from LHC p-Pb collisions. The new analysis will also involve recent JLab data for deeply-inelastic scattering. As a novel aspect within our approach, we now intend to also chart the impact of proton PDF uncertaities on our extraction of nuclear PDFs.
We present a new determination of nuclear parton distributions based on fixed-target and collider data. On top of Deep-Inelastic Scattering and Drell-Yan considered in nNNPDF2.0, we include a number of new processes that constrain the nuclear gluons: single jet and dijet cross-sections from ATLAS and CMS, direct photon production from ATLAS, and charm production by LHC. We use NNLO perturbative QCD calculations for all processes included in the fit. The proton baseline, which nNNPDF3.0 reduces to in the limit A=1, is a variant of the upcoming global NNPDF4.0 determination of proton PDFs, which includes several processes constraining the gluon PDF. We plan to further explore some of the phenomenological implications of nNNPDF3.0.
W and Z boson production and Neutrino deep inelastic scattering (DIS) data are the two most important data sets for constraining the strange quark parton distribution function (PDF) and for flavor decomposition in PDF extractions in general. We extend the nCTEQ15 nuclear PDFs (nPDFs) by adding the recent W and Z production data from LHC in a nCTEQ framework-based global nPDF fit. We identify the new nPDF set as nCTEQ15WZ and use it as a starting point for a follow-up study in which we assess the compatibility of neutrino DIS data with charged lepton DIS. Specifically, we re-analyze neutrino DIS data from NuTeV, Chorus, and CDHSW, as well as dimuon data from CCFR and NuTeV. Special emphasis is placed on the normalization uncertainty and corrections from target mass, deuteron, and higher twist effect. To highlight the level of compatibility, different kinematic regions of the neutrino data are investigated and consistency with leading-twist factorization picture is discussed.
Pre-recorded 3min talk with one-on-one discussion session via Gather Town
High-$p_T$, multi-lepton events remain one of the most sensitive probes of new physics at the LHC. Despite this, multi-weak boson and top quark-associated production channels remain leading Standard Model backgrounds for these signatures. We present a new class of jet vetoes, one that is defined on an event-by-event basis, that precisely targets these so-called irreducible backgrounds and can significantly improve signal-over-background significance. The veto exhibits somewhat desirable theoretical properties and suggests a lesser need for high order jet veto resummation. Applications to searches for lepton number and lepton flavor violation at $\sqrt{s}=14$ and 100 TeV are shown.
Many theories beyond the Standard Model predict additional Higgs bosons or other resonances, either at lower or higher masses than the observed Higgs boson near a mass of 125 GeV. This talk presents searches for such new states in leptonic or photonic final states using the full LHC Run 2 dataset recorded with the ATLAS detector.
Lepton flavor violation (LFV) constitutes a clear signature of New Physics, and has been searched for in many experiments. We present recent results on LFV searches from the Belle experiment. The results include a search for B → K(*) l l', B → tau l, tau → p l l', tau → l gamma decays. We also cover the study on the lepton flavor universality. The results are based on the full data sample collected by Belle at KEKB asymmetric energy e+e- collider.
We present a comprehensive analysis of the potential sensitivity of the Electron-Ion Collider (EIC) to charged lepton flavor violation (CLFV) in the channel $ep\to \tau X$, within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). We compute the relevant cross sections to leading order and
perform simulations of signal and SM background events in various $\tau$ decay channels, suggesting simple cuts to enhance the associated estimated efficiencies.
To assess the discovery potential of the EIC in $\tau$-$e$ transitions, we
study the sensitivity of other probes of this physics across a broad range of energy scales, from $pp \to e \tau X$ at the Large Hadron Collider to decays of $B$ mesons and $\tau$ leptons.
Leptoquarks (LQ) are predicted by many new physics theories to describe the similarities between the lepton and quark sectors of the Standard Model and offer an attractive potential explanation for the lepton flavour anomalies observed at LHCb and flavour factories. The ATLAS experiment has a broad program of direct searches for leptoquarks, coupling to the first-, second- or third-generation particles. This talk will present the most recent 13 TeV results on the searches for leptoquarks and contact interactions with the ATLAS detector, covering flavour-diagonal and cross-generational final states.
The CLAS12 detector at Jefferson Lab produced the first results in SIDIS and DI-HADRON reactions. 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 paving the road to the EIC physics.
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.
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 rich physics program will be given, which includes number of planned measurements: a multi-dimensional mapping of semi-inclusive DIS asymmetries for tomography of the nucleon in momentum space in the high-x region and precision determination of the tensor charge; 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/psi 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 current status and the plan of the project will be discussed.
The goal of LHCspin is to develop, in the next few years, innovative solutions and cutting-edge technologies to access spin physics in high-energy polarized fixed-target collisions, by exploring a unique kinematic regime given by the LHC beam and by exploiting new probes.
This ambitious task poses its basis on the recent installation of SMOG2, the unpolarized gas target in front of the LHCb spectrometer. Specifically, the unpolarized target, already itself a unique project, will allow to carefully study the dynamics of the beam-target system, and clarify the potentiality of the entire system, as the basis for an innovative physics program at the LHC.
The forward geometry of the LHCb spectrometer (2$\lt\eta\lt$5) is perfectly suited for the reconstruction of particles produced in fixed-target collisions. This configuration, with center-of-mass energies ranging from $\sqrt{s}$=115 GeV in pp interactions to $\sqrt{s_{NN}}$=72 GeV in collisions with nuclear beams, allows to cover a wide backward rapidity region, including the poorly explored high x-Bjorken and high x-Feynman regimes. With the instrumentation of the proposed target system, LHCb will become the first experiment delivering simultaneously unpolarized beam-beam collisions at $\sqrt{s}$=14 TeV and polarized and unpolarized beam-target collisions.
The status of the project is presented along with a selection of physics opportunities.
Investigations of coherent production background and eA collision geometry using forward particles at the EIC
Wan Chang
Institute of Particle Physics, Central China Normal University, Wuhan 430079, China
and Department of Physics, Brookhaven National Laboratory, Upton, NY 11973, USA
changwan@mails.ccnu.edu.cn
The Electron-Ion Collider (EIC) is a next generation accelerator which will provide answers to burning questions in the field of nuclear physics. The EIC is a very versatile collider with a wide range of beam energies, polarizations, and species, as well as high luminosity, all required to precisely image quarks and gluons in spatial and momentum space and their interactions, to explore the new QCD frontier of strong color fields in nuclei – to understand how matter at its most fundamental level is made. One of the golden measurements at the EIC is coherent $J/\psi$ vector meson production in electron-nucleus (eA) scattering in order to obtain the spatial gluon density distribution in heavy nuclei. However, the background contamination from the incoherent process could be overwhelming; therefore, the background suppression in the experiment will be key for a successful measurement. We investigate the rejection of incoherent $J/\psi$ production by vetoing the nuclear breakup – through the decay protons, neutrons, and photons. A realistic estimate of the rejection power has been made based on the conceptual design of the interaction region and its detector acceptances and performances. Based on the same detector configurations, we also revisit the concept of defining the collision geometry in eA using forward produced neutrons. The study is based on the BeAGLE event generator, which is a hybrid model combining Pythia 6, DPMJet, and Fluka for simulating deep-inelastic scattering in electron-ion collisions. In addition studies comparing BeAGLE to existing ZEUS and E665 experimental data are also presented.
The SpinQuest (Fermilab E1039) experiment intends to perform the first high statistics measurement of the sea-quarks Sivers asymmetry. Specifically, the primary focus of the experiment is to utilize proton induced polarized Drell-Yan production of di-muon pairs to extract the sign and magnitude of the anti-u and anti-d quark Sivers functions. A nonzero asymmetry would present strong evidence for orbital angular momentum of sea-quarks: a possible contributor to the proton’s spin. The experiment will use the unpolarized 120 GeV beam from the Fermilab Main Injector in conjunction with newly developed solid polarized NH3 and ND3 targets. The produced di-muon pairs will be observed in the SeaQuest (Fermilab E906) muon spectrometer. After a brief introduction to the experiment and experimental apparatus, the current SpinQuest status and plans will be presented.
In hadronic collisions, beauty quarks are produced in hard-scattering processes with large momentum transfer. The production of hadrons containing beauty quarks provides a very important test of perturbative QCD calculations in pp collisions. The measurement of the production of beauty-strange mesons relative to that of beauty hadrons without strange-quark content is useful to study the fragmentation of beauty quarks into beauty mesons. Moreover, the measurement of beauty-hadron production in heavy-ion collisions is a unique tool to investigate the properties of the colour-deconfined medium created, the quark--gluon plasma (QGP). In particular, beauty quarks, being four times heavier than charm quarks, can be exploited to study the mass dependence of the in-medium energy loss.
In this contribution, the latest results about beauty-hadron production via non-prompt $\mathrm{D}^0$, $\mathrm{D}^+$, $\mathrm{D_s}^+$ and $\mathrm{J}/\psi$ mesons, as well as beauty-decay electrons and dielectrons in pp collisions at a centre-of-mass energy of $\sqrt{s} = 5.02$ TeV, and their comparison to pQCD calculations will be presented. The ratio of the beauty-quark fragmentation fraction to strange beauty mesons and that to non-strange beauty mesons will be compared to the same quantity for the charm sector and to previous measurements in $\mathrm{e^{+}e^{-}}$, $\mathrm{e^{\pm}p}$, and $\mathrm{p\overline{p}}$ collisions. The extrapolated $\mathrm{b\overline{b}}$ cross section per unit of rapidity at midrapidity obtained from these measurements will be compared to pQCD calculations with next-to-leading order accurancy with all-order resummation of next-to-leading logarithms (FONLL) and with next-to-next leading order (NNLO) accurancy. Finally, the production of non-prompt $\mathrm{D}^0$ mesons in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV will be compared to the one of prompt $\mathrm{D}^0$ mesons and to different theoretical models.
Droplets of quark-gluon plasma produced in heavy-ion collisions rapidly evolve expanding and cooling. During considerable part of this dynamics the system can be described within relativistic hydrodynamics. Recently, there were some attempts to include effects of the medium motion to the jet energy loss and jet modification calculations in a variety of models. Here we will present the first principle consideration of the medium motion effects on the jet broadening and soft gluon radiation within opacity expansion approach. We will show that the developed formalism can be also applied to derive the effects of in-medium fluctuations on a wide range of the jet observables at EIC.
Light meson measurements in high-energy proton-nucleus collisions provide a probe to study the physics of strongly interacting matter and the quark-gluon plasma. In particular, measuring the nuclear modification factor, where the particle production in p-A is compared to a baseline proton-proton reference which is scaled to account for nuclear geometry, provides important insight to the modification of nucleon structure functions in nuclei and a baseline for the observed strong suppression of hadron yields at high $p_{\rm T}$ in heavy-ion collisions.
In this talk, neutral pion and $\eta$ meson invariant differential yields and nuclear modification factors at mid-rapidity are presented with a $p_{\rm T}$ reach beyond 100 GeV/$c$ and up to $40$ GeV/$c$, respectively, and compared to theoretical model calculations. Both neutral mesons are measured via their diphoton decay channel in pp and p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ and $8.16$ TeV with the ALICE experiment at the CERN LHC. The analysis combines results from several partially independent reconstruction techniques where the decay photons were detected with the electromagnetic calorimeter, EMCal, the photon spectrometer, PHOS, or via reconstruction of $e^+e^-$ pairs from conversions in the ALICE detector material using the central tracking system.
A. SHABETAI (for the ALICE Collaboration)
The measurement of jet production and structure observables in pp collisions provides significant tests of perturbative QCD. Jet measurements in proton-lead collisions enable study of cold nuclear matter effects. Jets are generated in the early stages of ultra-relativistic heavy-ion collisions and provide unique channels for probing the quark-gluon plasma (“jet quenching”). The ALICE Collaboration at the LHC has developed novel techniques for jet measurements in all such collision systems, with phase space coverage that is complementary to that of ATLAS and CMS. I will present an overview of recent ALICE jet measurements in the areas of jet production, jet structure, cold nuclear matter studies, and jet quenching.
Using the unification of chiral SU(3) model and QCD sum rules, we deduce the in-medium properties of $K^\pm_1$ meson. Within chiral SU(3) model, medium modified gluon and quark condensates are evaluated through their interactions with the scalar fields ($\sigma$, $\zeta$, $\delta$ and $\chi$). These condensates are further used as input in the Borel transformed equations of QCD sum rules to evaluate the in-medium mass of strange $K^\pm_1$ meson. The in-medium property of above meson can be used to study the restoration of chiral symmetry in the nuclear matter.
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 challenge assumptions on charmed baryon formation and show a baryon-over-meson ratio dependency 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 charmed baryon-to-meson ratio in pp collisions invoke enhanced color reconnection mechanisms or coalescence (recombination) schemes, or expect a significant contribution to $\Lambda_c$ yield from decays of heavier charm-baryon states.
The ALICE detector is well suited to detect charmed baryons down to low $p_{\rm T}$ thanks to the excellent tracking capabilities and state-of-art particle identification. $\Lambda_c$ 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. The $\Sigma_c$ and $\Xi_c$ baryons via semi-leptonic or hadronic decay channels.
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 and the total charm production at LHC center-of-mass energies.
Two-particle azimuthal correlation has been proposed to be one of the most direct and sensitive channels to access the nonlinear gluon dynamics in nuclei. In hadron collisions at RHIC, forward particle production probes gluons at small momentum fraction where the gluon density rises sharply. During the 2015 RHIC run, STAR collected data for measuring azimuthal correlations of neutral pions detected with the Forward Meson Spectrometer (FMS, 2.6 ≤ η ≤ 4.0) in p+p, p+Au and p+Al collisions at √sNN = 200 GeV. In this talk, we will present the measurement of di-hadron correlations as a function of mass number A and transverse momenta (pT ) of both the trigger π0 (1.4 GeV/c < pT < 5 GeV/c) and the associated back-to-back π0 (1 GeV/c < pT < 2.8 GeV/c).
We present an update of the measurements of the azimuthal decorrelation angle between the leading jet and scattered lepton in deep inelastic scattering, with the ZEUS detector at HERA. The studied data was collected 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). 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 HERA kinematic region provides unique insight of nucleon structure to understand the small-$x$ region. Also, electron-proton collisions measurements allow clean access to the quark TMD PDF, in particular to final state effects. The azimuthal decorrelation angle obtained in these studies shows good agreement with predictions from QCD calculations within uncertainties; however, there are parts of the phase space for which deviations of up to 20% are observed. Dedicated theoretical predictions are to be tested in the future.
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 $−1.5 < \eta < 2.0$ and transverse momentum $0.1 < p_T< 5.0$ GeV and event multiplicities $N_{ch}$ up to six times larger than the average $\langle N_{ch} \rangle ≈ 5$. The two-particle correlations have been measured in terms of the angular observables $c_n{2} = 〈〈\cos nΔφ〉〉$, where $n$ is between 1 and 4 and $∆φ$ is the relative azimuthal angle between the two particles. Comparisons with available models of deep inelastic scattering, which are tuned to reproduce inclusive particle production, suggest that the measured two-particle correlations are dominated by contributions from multijet production. The dependence of the correlations as a function of $Q^2$ has also been studied as well as the correlations in photoproduction events ($Q^2 \approx 0$). The correlations observed here do not indicate the kind of collective behaviour recently observed at the highest RHIC and LHC energies in high-multiplicity hadronic collisions.
The ridge phenomenon found in high multiplicity pp and pPb collisions is one of the most important observations at the LHC. In such small systems, final state explanations become challenging. We study particle correlations in the Color Glass Condensate, which offers a weak coupling but non perturbative framework to study how correlations in the wave function of the incoming hadrons reflect on those in the final state. Considering a dilute-dense situation suitable for pA collisions, we compute the correlation between azimuthal asymmetries, specifically the squared second Fourier coefficient $v^2_2$, and the total multiplicity in the event. We also consider the correlation between $v^2_2$ and the mean squared transverse momentum of particles in the event. In both cases, we find that the correlations are generally very small, consistent with the observations. We also note an interesting sharp change in the value of $v^2_2$ and its correlations as a function of the width of the transverse momentum bin, related with a change of the dominance of Bose and HBT quantum correlations.
Reference: Tolga Altinoluk, Néstor Armesto, Alex Kovner, Michael Lublinsky and Vladimir V. Skokov, e-Print: 2012.01810 [hep-ph].
The finding of long rapidity range azimuthal correlations in small collision systems, pp and pA, at the LHC poses a crucial challenge for our understanding of hadronic and nuclear collisions at the highest available energies. In such small collisions systems the final state explanations standardly accepted in heavy ion collisions face conceptual problems and initial state alternatives have been explored. The Color Glass Condensate offers a weak coupling but non perturbative framework where the imprint on the final state of parton correlations in the wave functions of the incoming hadrons can be studied. Here we compute four gluon production in dilute-dense collisions in the CGC, considering only those contributions enhanced by the nuclear size but keeping all terms in the number of colours. We use the Wigner function approach to proceed analytically as far as possible and discuss its validity. We then analyse the four particle cumulant $c_2\{4\}$ and find it to be negative, thus providing a sensible second order Fourier coefficient.
Color charge correlations in the proton at moderately small x are
extracted from its light-cone wave function. ${\cal O}(g^2)$ corrections to the
leading order correlations due to perturbative emission of a gluon,
which is not required to be soft, have been accounted for. This
analysis provides initial conditions for Balitsky-Kovchegov
high-energy evolution of the dipole scattering amplitude which include
impact parameter and $\hat r\cdot \hat b$ dependence, dependence on $x_0$, and with
non-zero C-odd component due to three-gluon exchange.
The color charge correlators are found to exhibit non-trivial
dependence on impact parameter as well as on the relative transverse
momentum (or distance) of the gluon probes. We present selected
numerical results for the dependence of the dipole scattering
amplitude at $x \sim 0.01 - 0.1$ on $x, \vec b, \vec r$, and the azimuthal angle. The
color charge correlators constitute the basis for a variety of
exclusive and semi-inclusive processes in DIS.
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 AN in proton-proton collisions are of interest due to their sensitivity to quark-gluon correlations. In this talk I will discuss our results on the first global fit of SSA data from SIDIS, Drell-Yan, e+e− annihilation into hadron pairs, and proton-proton collisions. I will also report on a study based on these results of the impact the EIC will have on extracting the nucleon tensor charge. This is an important quantity that sits at the intersection of TMD studies, beyond the Standard Model physics, and lattice QCD.
The transversity distribution function, $h^{q}_{1}(x)$, a leading twist parton distribution function, is a fundamental component of the spin structure of the nucleon. $h^{q}_{1}(x)$ describes the distributions of transversely polarized quarks inside a transversely polarized nucleon, where x is the longitudinal8momentum fraction of the proton carried by quark q. It is loosely constrained by global fits. Being chiral odd, $h^{q}_{1}(x)$ can be accessed only when it is coupled with another chiral-odd partner, such as the spin-dependent Collins fragmentation function (FF) or the interference fragmentation function (IFF), which serves as a quark polarimeter. In transversely polarized proton-proton ($p^\uparrow p$) collisions, the resulting azimuthal correlation between the spin of the fragmenting quark and the final state single charged hadron in jets (involving Collins FF) or di-hadron (involving IFF) can be measured, which are sensitive to quark transversity. The STAR experiment at RHIC has previously measured IFF asymmetries for $\pi^+\pi^-$ pairs using $p^\uparrow p$ collision data from 2006 at $\sqrt{s}$= 200 GeV ($\int L dt$ = 1.8 $pb^{-1}$) and from 2011 at $\sqrt{s}$= 500 GeV ($\int L dt$ = 25 $pb^{-1}$) and Collins asymmetries for charged pions within jets from 2011 at $\sqrt{s}$= 500 GeV. Non-zero IFF and Collins asymmetries were reported which are consistent with predictions based on global analyses of $e^+ e^-$ and SIDIS data. In 2012 and 2015, STAR collected $\sim$ 14 $pb^{-1}$ $\sim$ 48 $pb^{-1}$ of $p^\uparrow p$ data at $\sqrt{s}$ = 200 GeV, respectively. These datasets provide the most precise measurements of the Collins and IFF asymmetries in $p^\uparrow p$ collisions at $\sqrt{s}$= 200 GeV to date, especially at the quark momentum fractions 0.1< x <0.4. We will present preliminary results for Collins asymmetries of identified pions, kaons, and protons in jets based on 2012 and 2015 $p^\uparrow p$ datasets and the status update for IFF asymmetries based on 2015 $p^\uparrow p$ dataset at $\sqrt{s}$= 200 GeV.
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 restriction to implement further 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.
We propose a new method for the extraction of transversity distributions from Semi-Inclusive Deep Inelastic Scattering (SIDIS) data. The $u$-quark and $d$-quark transversity distributions are usually extracted from spin asymmetry data in the SIDIS processes, where it has to be coupled with a chiral odd-partner, typically the Collins or the di-hadron fragmentation function. Motivated by a recent suggestion on the extraction of transversity distribution with the concept of difference asymmetries and their ratios, which avoid the requirement of Collins function, we suggest a new measurement involving ratios of cross-sections, that would directly give the ratio $h_1^{d_v}/h_1^{u_v}$. We also present numerical estimates.
Quasi-PDF approach, proposed by Ji in 2013, has made it possible to directly extract light-cone PDFs from lattice QCD. This approach relies on the extraction of matrix elements of space-like operators for fast-moving hadrons. Quasi-PDFs can be related to the light-cone PDFs through a perturbatively calculable matching coefficient. We explore the formalism of matching, for the very first time, for the twist-3 PDFs $g_{T}(x)$, $e(x)$ and $h_{L}(x)$. In this talk, we address the non-trivialities involved in the extraction of the matching coefficient due to the presence of the zero-mode contributions.
Twist-3 PDFs contain important information that characterizes nucleon's structure. In this talk, we show our lattice exploration of the twist-3 PDFs g_T(x) and h_L(x). We use the quasi-distribution approach to connect the lattice-extracted matrix elements, renormalized in the RI/MOM scheme, to light-cone distributions, applying the matching procedure that we developed in parallel. We also calculate the twist-2 counterparts of these distributions and test the Wandzura-Wilczek approximation.
Gluon parton distribution functions (PDF) in protons and nuclei are known
to be difficult to determine with fits of deep inelastic scattering (DIS)
and Drell-Yan (DY) data alone. The nCTEQ15 analysis of nuclear PDFs
therefore resorted also to inclusive neutral pion production data from
RHIC. In this talk, we present a new global analysis of nuclear PDFs based
on a much larger set of single inclusive light hadron data from RHIC
and the LHC and study systematically the impact of the choice of the
fragmentation function.
We use the nCTEQ analysis framework to investigate nuclear Parton Distribution Functions (nPDFs) in the region of large x and intermediate-to-low Q, with special attention to recent JLab Deep Inelastic Scattering data on nuclear targets. This data lies in a region which is often excluded by W and Q cuts in global nPDF analyses. As we relax these cuts, we enter a new kinematic region, which requires new phenomenology. In particular, we will present the impact of i) target mass corrections, ii) higher twist corrections, iii) deuteron corrections, and iv) the shape of the nuclear PDF parametrization at large-x close to one. Using the above tools, we produce a new nPDF set (named nCTEQ15HIX) which yields a good description of the new JLab data in this challenging kinematic region, and displays reduced uncertainties at large x, in particular for up and down quark flavors.
We present the results that are necessary in the ongoing lattice calculations of the gluon parton distribution functions (PDFs) within the pseudo-PDF approach. We give a classification of possible two-gluon correlator functions and identify those that contain the invariant amplitude determining the gluon PDF in the light-cone $z^2\to0$ limit. One-loop calculations have been performed in the coordinate representation and in an explicitly gauge-invariant form. We made an effort to separate ultraviolet (UV) and infrared (IR) sources of the $\ln(−z^2)$-dependence at short distances $z^2$. The UV terms cancel in the reduced Ioffe-time distribution (ITD), and we obtain the matching relation between the reduced ITD and the light-cone ITD. Using a kernel form, we get a direct connection between lattice data for the reduced ITD and the normalized gluon PDF. We also show that our results may be used for a rather straightforward calculation of the one-loop matching relations for quasi-PDFs.
We present a lattice determination of pion valence parton distribution function (PDF) and electomagnetic form-factors. Our study use NNLO leading-twist perturbative matching formula to extract first few moments and reconstruct the x-dependent PDF of pion. Three mixed action ensambles including a physical pion mass with fine lattice spacings of a = 0.04, 0.06 and 0.076 fm are used to investigate the mass dependence as well as approaching continuum limit.
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 $a=0.091$ 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. A set of techniques are considered in order to ensure ground state dominance. Theoretical and experimental implications of our calculation are discussed.
In large-momentum effective theory, renormalization of
the Euclidean operators in lattice regularization is a challenge due to the linear divergences in the self-energy of Wilson lines.
Based on the Lattice QCD matrix elements of the quasi-PDF operator at $a$= 0.03fm $\sim$ 0.12 fm with clover and overlap valence quarks on staggered and domain-wall sea, we design a strategy to disentangle the divergent renormalization factors from finite physics matrix elements
which can be matched to a continuum scheme at short distance such as dimensional regularization and minimal subtraction. Our results
indicate that the renormalization factors are universal in the chiral fermion formalism but not in the clover case. However, the physical
matrix elements appear independent of the valence fermion formulations.
These conclusions remain valid after applying HYP smearing when the reductions of statistical errors are needed but a strict renormalization procedure becomes less clear.
Moreover, we find a large non-perturbative effect in the popular RI/MOM and ratio renormalization scheme used previously, which supports the hybrid
renormalization procedure proposed recently.
We present theoretical results with soft-gluon corrections for two separate processes: (1) the production of a single top quark in association with a W boson in the Standard Model; and (2) the production of a single top quark in association with a heavy Z' boson in new physics models with or without anomalous couplings. We show that the higher-order corrections from soft-gluon emission are dominant for a wide range of collider energies. Results are shown for the total cross sections and top-quark transverse-momentum and rapidity distributions for tW and tZ' production at LHC and future collider energies up to 100 TeV. The uncertainties from scale dependence and parton distribution functions are also analyzed.
The electro-weak interactions of the top quark are tested at the LHC by measurements of electro-weak single top quark production, of associated production processes of top quarks with gauge bosons and of top quark decay. In this contribution, the most recent ATLAS results are discussed, including measurements of the differential cross section for ttZ and ttgamma production using the full run 2 data set, new measurements of the single top cross section and polarization, and the recent observation of single top quark production with a neutral gauge boson. These measurements provide the first direct probe of the electro-weak couplings of the top quark and yield a valuable input to determine the parameters of the Standard Model Effective Field Theory.
The muon campus program at Fermilab includes the Mu2e experiment that will search for a charged-lepton flavor violating processes where a negative muon converts into an electron in the field of an aluminum nucleus, improving by four orders of magnitude the search sensitivity reached so far.
Mu2e’s Trigger and Data Acquisition System (TDAQ) uses {\it otsdaq} as its solution. Developed at Fermilab, {\it otsdaq} uses the {\it artdaq} DAQ framework and {\it art} analysis framework, under-the-hood, for event transfer, filtering, and processing.
{\it otsdaq} is an online DAQ software suite with a focus on flexibility and scalability, while providing a multi-user, web-based, interface accessible through a web browser.
The detector Read Out Controller (ROC), from the tracker and calorimeter, stream out zero-suppressed data continuously to the Data Transfer Controller (DTC). Data is then read by a software filter algorithm that selects events considering data flux that comes from a Cosmic Ray Veto System (CRV).
A Detector Control System (DCS) for monitoring, controlling, alarming, and archiving has been developed using the Experimental Physics and Industrial Control System (EPICS) Open Source Platform.
The DCS System has also been integrated into {\it otsdaq}. A prototype of the TDAQ and the DCS systems has been built at Fermilab’s Feynman Computing Center.
We report the developments and achievements of the integration of Mu2e’s DCS system into the online {\it otsdaq} software.
Building upon the most recent CT18 global fit, we present a new calculation of the photon content of proton based on an application of the LUXqed formalism. In this work, we explore two principal variations of the LUXqed ansatz. In one approach which we designate CT18lux, the photon PDF is calculated directly using the LUXqed formula for all scales, $Q$. In an alternative realization, CT18qed, we instead initialize the photon PDF in terms of the LUXqed formulation at a lower scale, $Q\! \sim\! Q_0$, and evolve to higher scales with a combined QED kernel at $\mathcal{O}(\alpha),~\mathcal{O}(\alpha\alpha_s)$ and $\mathcal{O}(\alpha^2)$.
While we find these two approaches generally agree, especially at intermediate $x$ ($10^{-3}< x<0.3$), we discuss some moderate discrepancies that can occur toward the end-point regions at very high or low $x$. We also study effects that follow from variations of the inputs to the LUXqed calculation originating outside the purely DIS region, including from elastic form factors and other contributions to the photon PDF. Finally, we investigate the phenomenological implications of these photon PDFs at the LHC, including high-mass Drell-Yan, vector-boson pair, top-quark pair, and Higgs$+$vector-boson production.
A multi-TeV muon collider is a discovery machine and an invaluable tool for many precision measurements such as the shape of the Higgs boson potential. The update of the European Strategy for Particle Physics recognized the unique opportunity of a muon collider to reach the energy frontier, despite the challenges to produce intense cooled muon beams. A 3 TeV and a 10+ TeV collider option is the main focus of the forming international collaboration, as well under discussion during the ongoing US Snowmass process.
The Design Study will identify the key issues and risks, the R&D priority plan and will provide a baseline concept for a muon collider facility (machine, experiment and machine detector interface) with well-supported performance expectations to ensure the overwhelming scientific merits. The status of the project, future plans and synergies will be discussed.
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 the full available Belle II data set, and the prospects for physics at Belle II.
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 LHeC Conceptual Design Report update [1].
[1] LHeC Collaboration and FCC-he Study Group, P. Agostini et al., e-Print: 2007.14491 [hep-ex].
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). Progresses of heavy flavor hadron and jet reconstruction in simulation and the corresponding physics projection such as the flavor dependent hadron nuclear modification factor in electron+nucleus collisions and flavor dependent jet angularity distributions in electron+proton collisions will be presented. Initial design and performance of a proposed forward (proton/nuclei going direction) silicon tracking detector, which is essential to carry out these measurements at the EIC will be discussed as well.
Generalised parton distributions are a key tool to study the three-dimensional structure of the nucleon. They shed light on its spin structure and energy-momentum tensor properties, and motivate numerous experimental programs involving hard exclusive experiments. Based on a next-to-leading order analysis, we exhibit non-trivial generalised parton distributions with arbitrarily small imprints on deeply virtual Compton scattering observables. This means that in practice the reconstruction of generalised parton distributions from measurements, known as the deconvolution problem, does not possess a unique solution for this channel. We discuss the consequences on the extracting strategies of generalised parton distributions from experimental data. We also advocate the necessity of a multi-channel analysis and emphasize the need for future electron-ion colliders.
Jets are algorithmic proxies of hard scattered partons, i.e. quarks/gluons, in high energy collisions. Current jet measurements utilize algorithms that cluster objects, either particles from an event generator or charged tracks/calorimeter towers in experiments, iteratively depending on the distance between objects and a momentum threshold. These clustering algorithms contain additional information regarding the jet shower that has been exploited in vacuum, i.e. in $pp$ collisions, via the SoftDrop algorithm to provide a handle on the jet shower via its splitting. The STAR collaboration has recently measured jet sub-structure observables in $pp$ collisions at $\sqrt{s} = 200$ GeV including the jet mass ($M$), SoftDrop groomed jet mass ($M_{g}$), groomed jet radius ($R_{g}$) and shared momentum fraction ($z_{g}$) for jets with varying jet radius and momentum. To further explore the jet sub-structure, we present the first measurement of the jet shower at the first, second and third splits via the iterative SoftDrop procedure. For each of these splits, we measure the fully corrected $z_{g}$ and $R_{g}$. We also showcase virtuality evolution in both the angular and momentum scales in data. These recursive measurements of the jet shower allow us to test the self-similarity of the DGLAP splitting function. The relatively low jet transverse momenta at RHIC energies, compared to those at the LHC, implies we are less sensitive to next-to-leading order effects on the jets themselves, but the corrections due to non-perturbative effects end up quite significant especially as we probe further along the jet shower history. We compare our measurements to current state-of-the-art Monte Carlo models, providing stringent constraints on model parameters related to the shower and non-perturbative effects such as hadronization. These measurements serve as a first step towards identifying and tagging jets based on their shower characteristics.
We propose the inclusive hadroproduction of a heavy-light dijet system, as a new channel for the investigation of high energy QCD. We build up an hybrid factorization that incorporates a partial next-to-leading BFKL resummation inside the standard collinear description of observables. We present a detailed analysis of different observables: cross-section summed over azimuthal angles and differential in rapidity, ratio of azimuthal coefficients differential in rapidity, heavy-jet transverse momentum distribution and azimuthal distribution. The stability that these distributions show under higher-order corrections motivates our interest in future studies. Here, the hybrid factorization could help to deepen our understanding of heavy-flavor physics in wider kinematic ranges, like the ones accessible at the Electron-Ion Collider.
Jets are collimated sprays of hadrons created by the fragmentation of high energy partons, and serve as an experimental tool for studying quantum chromodynamics. In particular, we can explore the properties of parton showers and jet evolution by measuring jet sub-structure. One of the techniques that allows experimental access to the parton shower is the jet grooming technique called SoftDrop. This analysis extends recent measurements of the jet sub-structure observables based on the SoftDrop algorithm in p+p collisions at $\sqrt{s}$ = 200 GeV in the STAR experiment, including groomed radius ($R_{g}$), shared momentum fraction ($z_{g}$) and splitting scale ($k_{T}$). We present fully unfolded multi-differential measurements of jet sub-structure observables at the first split and their corresponding correlations via $z_{g}$ vs. $R_{g}$ and $z_{g}$ vs. $k_{T}$ for jets of different transverse momenta and radii. With these measurements, we present the correlations between the physics scales involved with jet evolution for the first time. We compare our measurements to the state-of-the-art Monte Carlo models. We discuss the impact of variations in parton shower (perturbative) and hadronization/underlying-event (non-perturbative) modeling on the measured correlations between sub-structure observables.
The LHCb experiment at the Large Hadron Collider (LHC) is suited for studying how hadrons are formed from scattered quarks and gluons, collectively referred to as partons, in energetic proton-proton collisions. The hadronization process, conventionally described in terms of non-perturbative fragmentation functions in collinear factorization, can be learned in full picture at present via measurements such as those involving jet substructure. Fragmentation jet functions within the framework of jet substructure factorization provide access to transverse momentum dependent fragmentation functions (TMD FF's) which characterize multi-dimensional hadronization processes, and their flavor dependence within jets. Equipped with a forward spectrometer, the LHCb experiment achieves a transverse momentum resolution of $\frac{\Delta p_T}{p_T}< $1\% up to 200~GeV/c for charged tracks and a jet $p_T$ resolution of $<$15\%. This along with excellent particle identification capabilities offers a unique opportunity to measure with great precision hadronization variables $j_T$, z and r in TMD FF's. This talk will present published results for measurements of nonidentified hadrons within light quark-initiated jets as well as the status of other ongoing hadronization measurements at LHCb.
Measurements of the internal properties of jets allow QCD to be studied in a new energy regime. In this talk, we discuss recent measurements of jet substructure and jet fragmentation, which 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.
The Precision Proton Spectrometer (PPS) started operating in 2016 and has collected more than 110 fb−1 of data over the course of the LHC Run 2, now fully available for physics analysis. The talk will discuss the key features of PPS alignment and optics calibrations developed from scratch. The reconstructed proton distributions, performance of the PPS simulation and finally validation of the full reconstruction chain with physics data (dilepton events) will be shown.
We present the forward rapidity gap spectra from proton-lead (pPb) collisions for both pomeron-Pb and pomeron-p topologies measured at CMS. The analysis is performed over 10.4 units of pseudorapidity at a center-of-mass energy of 8.16 TeV, almost 300 times higher than previous measurements of diffractive production in proton-nucleus collisions. For the pomeron-Pb topology, the cross-section predicted by EPOS-LHC is a factor of two lower than the measured data while the model gives a reasonable description of the shape of the spectrum. For the pomeron-p topology, the EPOS-LHC, QGSJET II, and HIJING generator predictions are lower than the data by at least a factor of five. This effect can be explained by a significant contribution of ultra-peripheral photoproduction events mimicking the signature of diffractive processes. The obtained data may be of significant input for understanding the high energy limit of QCD and modeling cosmic ray air showers.
Possibilities for inclusive diffraction in electron-proton/nucleus collider, EIC in the US are analyzed. We find that thanks to the excellent forward proton tagging, the EIC will be able to access the wider kinematical range of longitudinal momentum fraction and momentum transfer of the leading proton than at HERA. This opens up the possibilities of measurement of subleading diffractive exchanges. The extended t-range would allow for the precise extraction of 4-dimensional reduced cross section in diffraction. In addition the varying beam setups at EIC would allow for precise measurements of longitudinal diffractive structure function. In the nuclear case EIC would be the first experiment to allow for the precise extraction of the nuclear diffractive parton distribution functions. In this talk we shall present a set of wide range of detailed studies of inclusive diffraction at the Electron Ion Collider and discuss the requirements on the experimental setup.
We show that the cross section for the diffractive dissociation of a small onium off a large nucleus conditioned to a minimum rapidity gap can be identified to a simple classical observable on the stochastic process representing the quantum evolution of the onium in the QCD dipole model. This holds true in the parametric limit defining the geometric scaling region. Such an identification authorizes the derivation of an analytical expression for the asymptotic gap distribution. Interestingly enough, events in which a large number of dipoles interact simultaneously bring a sizable contribution to the diffractive cross sections, which we are able to characterize quantitatively.
In this talk we present various measurements sensitive to non-perturbative physics performed using data collected by the ATLAS experiment at the LHC. 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 central detector. 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, this talk will also present the underlying event measurements using strange particles as probes.
We present results on the inclusive and identified (pion, kaon, proton and their antiparticles) charged-particle production in single diffractive dissociation process in proton-proton collisions at $\sqrt{s}= 200$ GeV with the STAR detector at RHIC. The forward-scattered proton is measured in the Roman Pot system, while the charged particle tracks are reconstructed in the STAR Time Projection Chamber (TPC). Ionization energy loss of charged particles in TPC is used for particle identification.
The proton-antiproton production asymmetry is measured as a function of transverse momentum ($p_{\mathrm{T}}$) and invariant mass of diffractive system, and used to study the baryon number transfer over a large rapidity interval in single diffractive dissociation process. In addition, $K/\pi$ ratio is measured, showing a larger strangeness production at $p_{\mathrm{T}} > 0.5$ GeV/c compared to measurements in inclusive proton-proton collisions.
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 $\pi^0$ ($2 < \eta < 4$) was brought up. Bigger asymmetry was observed in 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 role of the non-perturbative interaction in more detail. We installed a new electromagnetic calorimeter at the zero-degree area of the STAR experiment at the Relativistic Heavy Ion Collider 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 $p_T < 1$ showing a similar $x_F$ dependence with the forward $\pi^0$ one as the $p_T$ approached to 1 GeV/$c$. The non-perturbative interaction may induce its own non-zero asymmetry and there may be also a non-negligible contribution from it in the forward $\pi^0$ asymmetry. We present the first measurement of the very forward $\pi^0$ asymmetry and its result. A future aspect to more precisely study both of the perturbative and non-perturbative contribution will be also discussed.
Hard exclusive meson production is a well established tool to study the 3D nucleon structure in terms of the transverse position and the longitudinal momentum component of the partons. The QCD factorisation mechanism in the "nearly forward region" ($t/Q^{2}$ small) can be divided into a hard part, described by perturbative QCD (pQCD) and in two general structure functions, the GPDs for the nucleon and the pion distribution amplitudes (DAs), describing the complex non perturbative structure of these particles. In the "nearly backward" kinematic region ($u/Q^{2}$ small) the potentially applicable collinear factorized description in terms of a convolution of the non-perturbative nucleon to pion transitions (TDAs), the nucleon DAs and the hard interaction amplitude from pQCD is assumed to be valid. The talk presents a measurement of single beam spin asymmetries to extract ALUsinφ moments from the hard exclusive π$^+$ channel off the unpolarized hydrogen target in a wide range of kinematics from forward angles to backward angles in the center of mass frame based on data taken with the CLAS spectrometer at Jefferson Lab. The results clearly show that the sign of forward beam spin asymmetry measurements is positive whereas that of backward BSA measurements is negative, with the sign transition taking place around 90°. By performing accurate measurements over a wide range of $Q^2$, $x_B$ and $-t$, we can explore the transition from hadronic to partonic reaction mechanisms. In addition, for the GPD regime a detailed multidimensional study will be presented based on CLAS12 data and discussed based on a comparison to theoretical calculations.
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.
We will present results on Spin Density Matrix Elements (SDMEs) measured in hard exclusive $\rho^{0}$ meson muoproduction on the proton at COMPASS using 160 GeV/c polarised $\mu^{+}$ and $\mu^{-}$ beams scattering off a liquid hydrogen target. The measurement covers the range 5 GeV/$c^{2}$ < $W$ < 17 GeV/$c^{2}$, 1.0 (GeV/$c$)$^{2}$ < Q$^{2}$ < 10.0 (GeV/$c$)$^{2}$ and 0.01 (GeV/$c$)$^{2}$ < $p_{T}^{2}$ < 0.5 (GeV/$c$)$^{2}$. Here, Q$^{2}$ denotes the virtuality of exchanged photon, $W$ the mass of final hadronic system and p$_{T}$ the transverse momentum of the $\rho^{0}$ meson with respect to the virtual-photon direction. The kinematic dependences of SDMEs and of related observables will be presented. The measured non-zero SDMEs for transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ($\gamma^{*}_{T} \rightarrow V_{L}$) indicate a significant violation of $s$-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a small contribution of unnatural-parity-exchange transitions at small values of W. The results provide important input for modelling Generalised Parton Distribution (GPDs). In particular, they may allow to evaluate in a model-dependent way the role of parton-helicity flip GPDs ("transversity GPDs") in exclusive $\rho^{0}$ production.
Photoproduction of two photons is the simplest example allowing the study of QCD factorization in a family of $2\rightarrow 3$ processes. Because of the C-symmetry, the amplitude is sensitive only to valence quarks GPDs, which makes it interesting for the GPD extraction program. Leading-order calculation, presented in [1], and the subsequent work concerning electroproduction of 2 photons [2], suggest that this process may be experimentally accessible in JLAB.
I will present a new calculation of NLO corrections [3], which provide more accurate predictions and proof of factorization for this process at the one-loop level. I will also discuss the analytical structure of the amplitude, which is way richer than the one of DVCS and TCS cases.
[1] A. Pedrak, B. Pire, L. Szymanowski, and J. Wagner: Hard photoproduction of a diphoton with a large invariant mass, Phys. Rev. D 96 (2017), 074008, Erratum Phys. Rev. D 100 (2019), 039901
[2] A. Pedrak, B. Pire, L. Szymanowski, and J. Wagner: Electroproduction of a large invariant mass photon pair, Phys. Rev. D 101 (2020) 11, 114027
[3] O. Grocholski, B. Pire, L. Szymanowski, and J. Wagner, in preparation.
In spectator tagged process on a nucleus, a nucleon or nuclear fragment is detected in the target fragmentation region where the spectator has a slow (0 - few 100 MeV) momentum compared to the ion center-of-mass. Detection of the spectator results in additional control over the initial nuclear configuration of the ion target compared to inclusive scattering where one averages over all possible onfigurations. We discuss the theoretical framework used to describe spectator tagged reactions, which is based on light-front quantization and results in a natural separation of nuclear and nucleon structure. We focus on applications with the deuteron (free neutron structure and deuteron short-range structure using tensor polarization) and discuss the structure of the polarized tagged cross sections. We comment on the treatment of final-state interactions and extensions to targets beyond the deuteron.
We discuss strategies for comparisons of nonperturbative and lattice QCD predictions for collinear PDFs at large partonic momentum fractions x with high-energy experiments. While nonperturbative approaches offer increasingly complete predictions about the nucleon and meson structure at energies below 1 GeV, experimental measurements at energies above 1 GeV rely on perturbative QCD factorization. Using the CT18 NNLO global analysis as an example, we point out comparison strategies that are more informative when bridging the low- and high-energy formalisms and controlling for systematic effects. We compare effective power laws of the (1-x) dependence obtained from a global fit with predictions of quark counting rules. We also demonstrate that analytic predictions for functional forms for PDFs are not uniquely determined from the typical DIS and Drell-Yan data because of a mathematical property of mimicry of PDF parametrizations that we investigate using a representation based on Bézier curves.
We point out a problem in the phenomenological definition of the valence partons inside the proton. Parton degrees of freedom are definitively classified in the Euclidean path-integral formulation of the hadronic tensor in QCD. They include the valence and connected sea partons, the connected sea antipartons, and the disconnected sea partons and antiprotons. We resolve the problem by showing that the proper definition of the valence partons should be in terms of those in the connected insertions only. It is advocated that the connected sea and the disconnected sea should be separated in the global analysis of the PDFs. This allows a direct comparison of moments of PDF with the individual lattice matrix elements for the u, d, and s partons in the connected and disconnected insertions respectively.
In this study, the separation of the connected and disconnected sea partons is accommodated with the CT18 parametrization of the global analysis of the parton distribution functions (PDFs). This is achieved with the help of the distinct small x behaviors of these two sea partons and the constraint from the lattice calculation of the ratio of the strange momentum fraction to that of the $\bar u$ or $\bar d$ in the disconnected insertion. We compare the resulting PDFs of this new fit, using the same data set as the original CT18 fits, with the published CT18 family of PDFs. We also compare the predicted cross sections for $W^{\pm}$ and $Z$ productions at the LHC energies.
We present the results of a comprehensive new Monte Carlo analysis of high-energy lepton-lepton, lepton-hadron and hadron-hadron scattering data to simultaneously determine parton distribution functions (PDFs) in the proton and parton to hadron fragmentation functions (FFs). The analysis includes all available semi-inclusive deep-inelastic scattering and single-inclusive $e^+ e^-$ annihilation data for pions, kaons and unidentified charged hadrons, which allows the flavor dependence of the fragmentation functions to be constrained. Employing a new multi-step fitting strategy and more flexible parametrizations for both PDFs and FFs, we assess the impact of different data sets on sea quark densities, and confirm the previously observed suppression of the strange quark distribution.
LHC collisions can act as a source of photons in the initial state, in addition to the more standard quark and gluon initiated processes. This mechanism often plays an important role in the production of particles with electroweak couplings, and a precise account of photon-initiated (PI) production at the LHC is a key ingredient in the LHC precision physics programme. While one approach to treating this is to introduce a photon PDF, in line with the QCD partons, I will instead discuss the possibility of modelling PI processes directly via the so-called structure function approach. This makes no direct reference to PDFs and is (at least in certain cases) by construction more precise than the PDF approach. This in addition allows one to make use of another useful feature of photons, namely that they are colour-singlet and can often be emitted elastically (or quasi-elastically) from the proton. I will discuss recent work on applications of the structure function approach to precision calculations of PI production in the inclusive mode, and to 'exclusive' processes with rapidity gaps, which can provide a unique probe of the Standard Model and physics beyond it.
It is common lore that Parton Distribution Functions (PDFs) in the $\overline{\text{MS}}$ factorization scheme can become negative beyond leading order due to the collinear subtraction which is needed in order to define partonic cross sections. We show that this is in fact not the case and next-to-leading order (NLO) $\overline{\text{MS}}$ PDFs are actually positive in the perturbative regime. In order to prove this, we modify the subtraction prescription, and perform the collinear subtraction in such a way that partonic cross sections remain positive. This defines a factorization scheme in which PDFs are positive. We then show that positivity of the PDFs is preserved when transforming from this scheme to $\overline{\text{MS}}$, provided only the strong coupling is in the perturbative regime, such that the NLO scheme change is smaller than the LO term.
We propose a new factorized approach to QED radiative corrections (RCs) in inclusive and semi-inclusive lepton-hadron deep-inelastic scattering. The method allows the systematic resummation of the logarithmically enhanced into factorized lepton distribution and fragmentation (or jet) functions that are universal for all final states. The new approach provides a uniform treatment of RCs for the extraction of parton distribution functions, transverse momentum dependent distributions, and other partonic correlation functions from lepton-hadron collision data.
In the Standard Model, the branching ratio for Higgs boson decays to invisible final states is very small, but it can be significantly enhanced in extensions of the Standard Model. In addition, the observed Higgs boson could couple to new particles decaying into Dark Matter. This talk presents searches for Higgs boson decays to invisible final states or Dark Matter in association with the observed Higgs boson using the full Run 2 data recorded with the ATLAS detector.
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 Compact LInear Collider (CLIC) is a proposed TeV-scale high-luminosity electron-positron collider at CERN. CLIC will allow us to study the Higgs boson properties with very high precision. These measurements can also result in direct or indirect discovery of "new physics", Beyond the Standard Model (BSM) phenomena, which could help us to understand the nature of dark matter (DM). SM-like Higgs boson or new heavy scalar decays with emission of invisible DM particles can be the only way to observe "new physics" effects at achievable energy scales and establish connection between Standard Model (SM) and BSM sectors.
We studied the possibility of measuring invisible Higgs boson and additional heavy scalars decays with experiment at CLIC running at 380 GeV and 1.5 TeV. The analysis is based on the WHIZARD event generation and fast simulation of CLIC detector response with DELPHES. We estimated the expected limits on the invisible decays of the 125 GeV Higgs boson, as well as the cross section limits for production of an additional neutral Higgs scalar, assuming its invisible decays, as a function of its mass. Extracted model-independent branching ratio and cross section limits were then interpreted in the framework of the vector-fermion dark matter model to set limits on the mixing angle between the SM-like Higss boson and the new scalar of the "dark sector".
One of the primary goals of the proposed future collider experiments is to search for dark matter (DM) particles using different experimental approaches. High energy $e^+e^-$ colliders offer unique possibility for the most general search based on the mono-photon signature. As any $e^+e^-$ scattering process can be accompanied by a hard photon emission from the initial state radiation, analysis of the energy spectrum and angular distributions of those photons can be used to search for hard processes with invisible final state production and to test the nature and interactions of the DM particles. Dedicated procedure of merging the matrix element calculations with the lepton ISR structure function was developed to model the Standard Model background processes contributing to mono-photon signature with WHIZARD.
We consider production of DM particles at the International Linear Collider (ILC) and Compact Linear Collider (CLIC) experiments. Detector effects are taken into account within the DELPHES fast simulation framework. Limits on the light DM production in a generic model are set as a function of the mediator mass and width based on the expected two-dimensional distributions of the reconstructed mono-photon events. Limits on the mediator coupling to electrons are presented for a wide range of mediator masses and widths. For light mediators, for masses up to the centre-of-mass energy of the collider, results from the mono-photon analysis are more stringent than the limits expected from direct resonance search in SM decay channels.
Compact Linear Collider (CLIC) was proposed as the next energy-frontier infrastructure at CERN, allowing to study $e^{+}e^{-}$ collisions at three centre-of-mass energy stages: 380 GeV, 1.5 TeV and 3 TeV. The main goal of its high-energy stages is to search for the new physics beyond the Standard Model (SM). The Inert Doublet Model (IDM) is one of the simplest SM extensions and introduces four new scalar particles: $H^{\pm}$, $A$ and $H$; the lightest, $H$, is stable and hence it is a natural dark matter (DM) candidate. A set of benchmark points is considered, which are consistent with current theoretical and experimental constraints and promise detectable signals at future colliders.
Prospects of observing pair-production of the IDM scalars at CLIC were previously studied for signatures with two leptons in the final state. In the current study, discovery reach for the IDM charged scalar pair-production is considered for the semi-leptonic final state at the two high-energy CLIC stages. Full simulation analysis, based on the new CLIC detector model, is presented for five selected IDM scenarios. Results are then extended to the larger set of benchmarks using DELPHES fast simulation framework. The CLIC detector model for DELPHES has been modified to take pile-up contribution from the beam-induced $\gamma \gamma$ interactions into account, which is crucial for the presented analysis. Results of the study indicate that heavy, charged IDM scalars can be discovered at CLIC for most of the proposed benchmark scenarios, with very high statistical significance.
In this talk the current status and plans are presented on the LHeC,
towards the new HEP strategy update in about 5 years time, on physics,
with emphasis on the eh-hh relation, on the machine, especially the IR,
and further detector developments. The talk also covers FCC-eh and refers
to a separate presentation of the ERL facility PERLE. It is based on the
comprehensive CDR update which is being published in J. Phys. G [1].
[1] LHeC Collaboration and FCC-he Study Group, P. Agostini et al., e-Print: 2007.14491 [hep-ex].
The LUXE experiment (LASER Und XFEL Experiment) is a new experiment in planning at DESY Hamburg using the electron beam of the European XFEL. LUXE is intended to study collisions between a high-intensity optical LASER and 16.5 GeV electrons from the XFEL electron beam, as well as collisions between the optical LASER and high-energy secondary photons. The physics objective of LUXE are processes of Quantum Electrodynamics (QED) at the strong-field frontier, where the electromagnetic field of the LASER is above the Schwinger limit. In this regime, QED is non-perturbative. This manifests itself in the creation of physical electron-positron pairs from the QED vacuum, similar to Hawking radiation from black holes. LUXE intends to measure the positron production rate in an unprecedented LASER intensity regime. An overview of the LUXE experimental setup is given, in the context within the field of high-intensity particle physics. The foreseen detector systems and their sensitivity are presented. Finally, the prospects for studying BSM physics are also discussed.
The data on tau neutrino is very scarce, only a few experiments have detected its interactions. At FNAL beam dump experiment DONUT, tau neutrino interaction cross-section was directly measured with a large systematical (~50%) and statistical (~30%) errors. The main source of systematical error is due to a poor knowledge of the tau neutrino flux. The effective way for tau neutrino production is the decay of Ds mesons, produced in proton-nucleus interactions. The DsTau experiment at CERN-SPS has been proposed to measure an inclusive differential cross-section of a Ds production with a consecutive decay to tau lepton in p-A interactions. The goal of experiment is to reduce the systematic uncertainty to 10% level. A precise measurement of the tau neutrino cross section would enable a search for new physics effects such as testing the Lepton Universality (LU) of Standard Model in neutrino interactions. The detector is based on nuclear emulsion providing a sub-micron spatial resolution for the detection of short length and small “kink” decays. Therefore, it is very suitable to search for peculiar decay topologies (“double kink”) of Ds→τ →X. After successful pilot runs and data analysis, CERN had approved the DsTau project as a new experiment NA65 in 2019. During the physics runs, 2.3×108 proton interactions will be collected in the tungsten target, and about 103 Ds→τ decays will be detected. In this talk, the results from the pilot run will be presented and the prospect for physics runs in 2021-2022 will be given.
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.
In the spin-1 deuteron, there are additional polarized structure functions which do not exist in the spin-1/2 nucleons. Especially, the gluon transversity appears as a new distribution in the deuteron. We proposed to investigate the gluon transversity distribution at hadron accelerator facilities [1]. Although there was recent experimental progress on quark transversity distributions, there is no experimental information on the gluon transversity. The gluon transversity does not exist for the spin-1/2 nucleons due to the helicity-conservation constraint. One needs a hadron with spin more than or equal to one, so that the helicity flip of two units is allowed. In our work, we proposed the possibility for finding the gluon transversity at hadron-accelerator facilities, especially in the proton-deuteron Drell-Yan process, by showing theoretical formalism and numerical results. This Drell-Yan experiment is under consideration in the Fermilab-E1039 experiment. The NICA project could also contribute to this topic. Since the internal spin-1/2 nucleons within the deuteron cannot contribute directly to the gluon transversity, it could be a good observable to find a new non-nucleonic component beyond the simple bound system of nucleons in nuclei.
The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for the origin of dark matter sharpen the focus on a narrower range of masses: the natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the DM mass to lie within about an MeV to 100 TeV. Considerable experimental attention has been given to exploring Weakly Interacting Massive Particles in the upper end of this range (few GeV – ~TeV), while the region ~MeV to ~GeV is largely unexplored. Most of the stable constituents of known matter have masses in this lower range, tantalizing hints for physics beyond the Standard Model have been found here, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well. It is therefore a priority to explore. If there is an interaction between light DM and ordinary matter, as there must be in the case of a thermal origin, then there necessarily is a production mechanism in accelerator-based experiments. The most sensitive way, (if the interaction is not electron-phobic) to search for this production is to use a primary electron beam to produce DM in ﬁxed-target collisions. The Light Dark Matter eXperiment (LDMX) is a planned electron-beam fixed-target missing-momentum experiment that has unique sensitivity to light DM in the sub-GeV range. This contribution will give an overview of the theoretical motivation, the main experimental challenges and how they are addressed, as well as projected sensitivities in comparison to other experiments.
In this contribution a measurement is presented of several observables that are sensitive to the fragmentation of b-quarks. The measurement is based on an analysis of 36 fb−1 of sqrt(s)=13 TeV LHC data. Jets containing b-hadrons are obtained from a sample of dileptonic ttbar events. The associated set of charged-particle tracks is separated into those from the primary pp interaction vertex and those from the displaced b-decay secondary vertex and used to construct high-resolution observables which characterize the longitudinal and transverse momentum distributions of the b-hadron within the b-jet. The corrected results are found to agree with the predictions of modern Monte Carlo parton-shower generators. These measurements complement similar measurements from e+e− collider experiments in which the b-quarks originate from a color-singlet Z/γ∗.
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-𝜒 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 𝑝𝑇→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± production at 7 and 13 TeV.
Measurements of the properties of b-hadrons and quarkonia can help deepen our understanding of strong interaction. The large b- and c-hadron yields at LHCb and excellent performance of the LHCb detector make it an ideal laboratory for such studies. This talk presents the recent experimental studies on production, decay and spectroscopy of conventional b-hadrons and quarkonia at LHCb.
In this talk we discuss different mechanisms of open-heavy flavor meson and heavy quarkonia production which contribute to inclusive and single diffractive (SD) cross-sections.
For the case of inclusive production of open heavy flavor mesons, we evaluated explicitly the contributions of the two-Pomeron and the three-Pomeron fusion. We found that the latter mechanism is significant for the D-meson production in the kinematics of small transverse momenta pT and helps to significantly improve the description of experimental data. Its role is less important at larger pT, as well as for B-mesons. Contrary to naive expectations, the contribution of the three-Pomeron mechanism has only mild effect on the multiplicity dependence of the self-normalized yields in the kinematic range studied recently by ALICE collaboration. We also analyzed the contribution of the single diffractive mechanism of the open heavy flavor mesons, and found that it constitutes 0.5–2 per cent of the inclusive cross-sections. Our theoretical results for SD production are in reasonable agreement with the available experimental data from Tevatron, and theoretical predictions in LHC kinematics indicate that the cross section is sufficiently large for experimental studies. The expected dependence on event multiplicity in this channel is significantly milder than for inclusive production.
Finally, for the quarkonia states we analyzed different production mechanisms and evaluated the expected multiplicity dependence for S-wave and P- wave quarkonia production. Using recent experimental data for J/ψ mesons from STAR and ALICE collaborations, we demonstrate that a rapidly growing multiplicity dependence presents a strong evidence in favor of multigluon fusion mechanisms of these quarkonia states. 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 ψ(2S) and Υ(1S), and demonstrate that their multiplicity dependence should be close to that of J/ψ. For 1P quarkonia states (χc, χb mesons), we found that the three-pomeron contribution does not contribute at high energies, and for this reason we predict that the multiplicity dependence of such states should be significantly milder than that of 1S quarkonia. We expect that the experimental confirmation of this result could constitute an important test of our understanding of multiplicity enhancement mechanisms in the production of different quarkonia states.
We believe that the experimental confirmation of all these predictions will help us to understand better the production mechanisms of different hadrons containing charm and bottom quarks.
This presentation is partially based on our recent publications Phys.Rev.D 101 (2020) 094020, Phys.Rev.D 102 (2020) 076020, Eur.Phys.J.C 80 (2020) 560 and arXiv submission https://arxiv.org/abs/2012.08284.
Recent results from the ATLAS experiment on the B_c production and decays will be presented. The measurement of the ratios of the B_c+ and B+ production cross sections in proton-proton collisions at 8 TeV will be discussed.
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 also focus on the latest results from ATLAS, such as rare processes: B^0_s → mu mu and B^0 → mu mu; and CPV in the B_s^0 —> J/psi phi decays. In the latter, the Standard Model predicts the CP violating mixing phase, phi_s, to be very small and its SM value is very well constrained, while in many new physics models large phi_s values are expected. Latest measurements of phi_s and several other parameters describing the B_s^0 —> J/psi phi decays will be reported.
We discuss mechanisms of dilepton production in proton-proton collisions with rapidity gap in the main detector and one forward proton in the forward proton detectors. This is relevant for LHC measurements by ATLAS+ALFA and CMS+TOTEM. The calculations are performed including transverse momenta of the virtual photons and using relevant off-shell matrix elements. Differential distributions in $\xi_{1/2}$, $M_{ll}$, $Y_{ll}$, $p_{t,ll}$ are shown and the competition of different mechanisms is discussed. Both double-elastic and single-dissociative processes are included in the calculation. We discuss also mechanism with one forward $\Delta^+$ isobar, or other proton resonances in the final state not discussed so far in the literature. The role of several cuts is studied. The rapidity gap survival factor is calculated for each contribution separately. The gap survival factor for the single-dissociative mechanism are calculated as due to minijet emission into the main detector. The corresponding gap survival factor depends on the invariant mass of the dilepton system as well as the mass of the proton remnant. The gap survival with and without proton measurement in forward proton detector are compared and the underlying dynamics is discussed. The dependence on the parametrization of the proton structure functions is shown in addition.
We present results on the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = \pi, K, p$) obtained in the STAR experiment at RHIC in proton-proton collisions at center-of-mass energy of $\sqrt{s} = 200$ GeV. All final-state particles of the process $pp\to p^\prime+h^{+}h^{-}+p^\prime$ were reconstructed, including forward-scattered protons detected in the Roman Pot system. As a result, the Double Pomeron Exchange (DPE) events were selected and the non-exclusive backgrounds were efficiently rejected.
Differential fiducial cross sections were measured as functions of observables related to the central hadronic final state and to the forward-scattered protons. The measured cross sections were compared to phenomenological predictions based on the DPE model. Structures observed in the mass spectra of $\pi^{+}\pi^{-}$ and $K^{+}K^{-}$ pairs were found consistent with the DPE model, while angular distributions of pions suggested a dominant spin-0 contribution to $\pi^{+}\pi^{-}$ production.
For $\pi^+\pi^-$ production, the fiducial cross section was extrapolated to the Lorentz-invariant region and was successfully modeled assuming the continuum production and at least three resonances, the $f_0(980)$, $f_2(1270)$, and $f_0(1500)$, with a possible small contribution from the $f_0(1370)$.
Fits to the extrapolated differential cross section as a function of squared four-momentum transfers in proton vertices enabled extraction of the exponential slope parameters in several bins of the invariant mass of $\pi^+\pi^-$ pairs. These parameters are sensitive to the size of the interaction region.
We also present preliminary results on the measurement of the same physics process at higher $\sqrt{s} = 510$ GeV. The data demonstrate features similar to those observed at $\sqrt{s} = 200$ GeV.
Exclusive emissions of vector mesons in forward directions of rapidity offer us a faultless chance to probe the proton structure at small-$x$. Here, a high-energy factorization formula is established within the Balitsky-Fadin-Kuraev-Lipatov (BKFL), given as the convolution of a impact factor depicting the forward-meson emission and of an unintegrated gluon distribution (UGD) driving the gluon evolution at small-$x$. Being a nonperturbative quantity, the UGD is not well known and several models for it have been proposed so far. We present recent progresses on the study of exclusive emissions of forward $\rho$-mesons in lepto-hadronic collisions, showing how osbervables sensitive to different polarization states of the $\rho$-particle act as discriminators for the existing UGD models.
Exclusive photoproduction of $\rho^0(770)$ mesons is studied using the H1 detector at the $ep$ collider HERA. A sample of about 900000 events is used to measure single- and double-differential cross sections for the reaction $\gamma p\to \pi^{+}\pi^{−}Y$. Reactions where the proton stays intact ($m_Y=m_p$) are statistically separated from those where the proton dissociates to a low-mass hadronic system ($m_p\lt m_Y \lt 10$ GeV). The double-differential cross sections are measured as a function of the invariant mass $m_{\pi\pi}$ of the decay pions and the squared 4-momentum transfer $t$ at the proton vertex. The measurements are presented in various bins of the photon-proton collision energy $W_{\gamma p}$. The phase space restrictions are $0.5\lt m_{\pi\pi}\lt 2.2$ GeV, $|t|\lt1.5$ GeV$^2$, and $20\lt W_{\gamma p}\lt 80$ GeV. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the $m_{\pi\pi}$ dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the $\rho^0(770)$ meson mass and width at $m_{\rho}=770.8^{+2.6}_{-2.7}$ (tot.) MeV and $\Gamma_{\rho}=151.3^{+2.7}_{-3.6}$ (tot.) MeV, respectively. The model is used to extract the $\rho^0(770)$ contribution to the $\pi^{+}\pi^{−}$ cross sections and measure it as a function of $t$ and $W_{\gamma p}$. In a Regge asymptotic limit in which one Regge trajectory $\alpha(t)$ dominates, the intercept $\alpha(t=0)=1.0654^{+0.0098}_{−0.0067}$ (tot.) and the slope $\alpha′(t=0)=0.233^{+0.067}_{−0.074}$ (tot.) GeV$^{−2}$ of the $t$ dependence are extracted for the case $m_Y=m_p$.
Eur.Phys.J.C80 (2020), 1189 [arxiv:2005.14471]
Lead ions circulating in the LHC provide copious photonuclear interactions.
These dominate the interaction rate via ultra-peripheral collisions (UPC),
when the impact parameter of the colliding lead ions is larger than the sum of their radii.
The study of \rho^0 meson photonuclear production is important,
because its cross section in 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 and in Xe--Xe UPC at sqrt(s_NN)=5.44 TeV are presented.
Both the Pb--Pb and Xe--Xe 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 measurements were used to determine the A dependence at W\gamma-p=65 GeV.
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.
Exclusive scattering processes are especially powerful probes of the proton and nuclear structure at small $x$. In particular, the possibility to measure the total momentum transfer allows for the extraction of the spatial distribution of small-$x$ partons, including their event-by-event fluctuations[1].
More detailed information about the target structure can be obtained by studying more differential observables. In our recent work [2] presented in this talk, we study coherent diffractive photon and vector meson production in electron-proton and electron-nucleus collisions within the Color Glass Condensate effective field theory focusing on the azimuthal angle correlations between the outgoing lepton and the produced vector particle. We show that the azimuthal angle correlations are sensitive to non-trivial spatial correlations in the gluon distribution of the target, and perform explicit calculations using spatially dependent McLerran-Venugopalan initial color charge configurations coupled to the numerical solution of small $x$ JIMWLK evolution equations. We compute the cross-section differentially in $Q^2$ and $|t|$ and find sizeable anisotropies in the electron-photon and electron-J/ψ azimuthal correlations ($v_{1,2}≈2−10\%$) in electron-proton collisions for the kinematics of the future Electron-Ion Collider. In electron-gold collisions these modulations are found to be significantly smaller ($v_{1,2}<0.1\%$). We also compute incoherent diffractive production where we find that the azimuthal correlations are sensitive to fluctuations of the gluon distribution in the target.
[1] See e.g. H. Mäntysaari, Rept.Prog.Phys. 83 (2020) 8, 082201, arXiv:2001.10705 [hep-ph] for a review
[2] H.Mäntysaari, K. Roy, F. Salazar, B. Schenke, arXiv:2011.02464 [hep-ph]
In this talk we will outline the connections among the inclusive jet correlator, the single-hadron fragmentation correlator, and the quark propagator, which open the way to studies of fundamental mechanisms in QCD -such as the dynamical generation of mass- by looking at the fully inclusive hadronization of a quark. In particular, we will focus on observables in semi-inclusive DIS and $e^+e^-$ annihilation at the twist three level.
The Solenoidal Tracker at the Relativistic Heavy Ion Collider (STAR) experiment probes the gluon helicity distribution $\Delta g(x, Q^2)$ using collisions of longitudinally polarized protons at $\sqrt{s} = 200$ GeV and $\sqrt{s} = 510$ GeV. $\Delta g(x, Q^2)$ can be accessed through the double spin asymmetries $A_{LL}$ in gluon-dominated hard scattering processes via inclusive jet and di-jet production.
Previously published results on inclusive jet production at $\sqrt{s}=200$ GeV and mid-pseudorapidity $|\eta_{\mathrm{jet}}| < 1$ are based on data corresponding to an integrated luminosity $L = 20$ pb$^{-1}$ with an average beam polarization $P = 57\%$. When included in perturbative QCD analysis of global data, they provide evidence for positive gluon polarization for the momentum fraction $x > 0.05$ at a hard perturbative scale $Q^2 = 10$ GeV$^2$. This talk will cover the inclusive jet and di-jet $A_{LL}$ measurements based on the most recent data with an approximately twice larger figure of merit, $LP^4$, and with improved systematic uncertainties, compared to the published results. The status of the jet $A_{LL}$ measurements at $\sqrt{s} =$ 510 GeV, which will constrain $\Delta g(x, Q^2)$ at lower $x$, will be also discussed.
Understanding the proton spin composition from the quarks and gluons spin polarization and their motion is important to test various kinds of sum rules and nonperturbative properties of hadrons. At the Relativistic Heavy Ion Collider (RHIC), we collide longitudinally polarized proton beams and measure the double helicity asymmetry $A_{LL}$, which is an important physical quantity for extracting the polarized parton distribution functions (PDFs) of the proton. Direct photon, jet and charged pion production are good channels to probe the gluon spin polarization inside the proton, with the ability to probe also the sign of the gluon spin. Direct photon production is the theoretically ``cleanest'' channel, with little fragmentation contribution, but limited by statistics. On the other hand, jet and charged pion production have more statistics, but include more hard processes and hadronization effects. In this talk, I will present the resent measurements of direct photon, jet and charged pion $A_{LL}$s at PHENIX and show their complementary roles in extracting the gluon spin.
We made simultaneous extraction of spin averaged and spin dependent PDFs within multistep MC procedures, with combined analysis of inclusive unpolarized and polarized Jet from RHIC to Tevatron energies. By analyzing the preliminary results we had, we were able to further constrain on $\Delta g$.
We present a new global QCD analysis of spin-averaged and spin-dependent PDFs from high-$x$ DIS and $W$ production data using a Monte Carlo approach. This analysis includes the first extraction of the helicity-dependent antiquark asymmetry $\Delta \bar{u} - \Delta \bar{d}$ using $W$ production data in $\vec{p} p$ collisions at RHIC. We also 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.
The small-$x$ quark helicity evolution equations at double-logarithmic order, with the kernel $\sim \alpha_s\ln^2 (1/x)$, had been derived previously, and the equations were solved analytically at large $N_c$ and numerically at large $N_c$ and $N_f$. (Here, $N_c$ and $N_f$ are the numbers of quark colors and flavors, respectively.) In this work, we derive the single-logarithmic corrections to the double-logarithmic equations derived previously, that is, we find the correction to order $\alpha_s\ln (1/x)$ of the evolution kernel. The new equations include the effects of the running coupling and the unpolarized small-$x$ evolution, both of which are parametrically significant at single-logarithmic order. The large-$N_c$ and large-$N_c \& N_f$ approximations to the equation are computed. Their solution will provide a more precise estimate of the quark helicity distribution at small $x$, contributing to the resolution of the proton spin puzzle.
We discuss the role of the chiral “triangle” anomaly in deeply inelastic scattering (DIS) of electrons off polarized protons employing a powerful worldline formalism which allows for the efficient computation of perturbative multi-leg Feynman amplitudes. We demonstrate how the triangle anomaly appears at high energies in the DIS "box diagram" for the polarized structure function $g_1(x_B,Q^2)$ in both the Bjorken limit of large $Q^2$ and in the Regge limit of small $x_B$. We show for the first time that the off-forward infrared pole of the anomaly appears in both limits. We motivate a small x effective action, consistent with anomalous chiral Ward identities, that shows how non-perturbative effects cancel the infrared pole, leading to an effective axion-like dynamics at small x. There are two non-perturbative scales that control this dynamics: one is the saturation scale and the other is the pure Yang-Mills topological susceptibility; we discuss how their dynamical interplay can be uncovered in polarized DIS at the Electron-Ion Collider.
References:
A. Tarasov and R. Venugopalan "Role of the chiral anomaly in polarized deeply inelastic scattering: Finding the triangle graph inside the box diagram in Bjorken and Regge asymptotics", Phys. Rev. D 102, 114022;
A. Tarasov and R. Venugopalan "The role of the chiral anomaly in polarized deeply inelastic scattering: Emergent axion-like dynamics and the small x effective action", in preparation.
A reanalysis of the model of longitudinal structure function FL(x, Q^2) at low x
and low Q^2 was undertaken, in view of the advent of the EIC. The model includes the kinematic constraint FL ∼ Q^4 as Q^2 → 0. It is based on the photon-gluon fusion mechanism suitably extrapolated to the region of low Q2.
The contribution of quarks having limited transverse momentum is treated phenomenologically assuming that it is described by the soft pomeron exchange mechanism. The ratio R = FL/(F2−FL), with the F2 appropriately extrapolated to the region of low Q^2, is also discussed. Revised models were critically updated, extended to the EIC kinematic region, and e.g. contain new parameterisations of the parton distribution functions.
The knowledge of both F2 and FL structure functions, from the photoproduction to the DIS region is needed in the procedure used to extract polarised and nonpolarised structure functions from the experimental data, especially in the calculations of QED radiative corrections. Thus both functions will be indispensable in the data analysis.
An experimental procedure is proposed to perform measurements of differential cross sections which can be compared to fixed-order QCD predictions with improved accuracy. The procedure can be applied to the Drell-Yan cross-section measurements which are differential in the boson transverse momentum. An example analysis is performed using the ATLAS measurement of the Z-boson production cross section at center-of-mass energy of 8 TeV. The resulting full phase space measurement of the cross section differential in the boson rapidity is compared to theoretical predictions computed with next-to-next-to leading-order accuracy in QCD.
(based on Eur. Phys. J. C 80, 875 (2020))
LHCb is a spectrometer that covers the forward region of proton-proton collisions, corresponding to the pseudo-rapidity range 2<eta<5. Thanks to its coverage, LHCb can probe the parton distribution functions (PDF) in a phase space region unexplored by other experiments, in particular in the low-x region. Moreover LHCb data could be used to test perturbative QCD predictions. In this context the production of a Z boson in association with a c-jet can be studied to measure the intrinsic charm content. Moreover several PDFs model and QCD calculations could be tested by studying the differential cross section of charged particles production. In this talk these measurements will be presented and 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. We also present the results of PDF fits that use Z+jets measurements from ATLAS in addition to the measurements listed above. An improved determination of the sea-quark densities at high Bjorken, x, is seen, while confirming a strange-quark density similar in size to the up- and down-sea-quark densities in the range x < 0.02 found by previous ATLAS analyses. If available, PDF fits including inclusive W and Z boson production, ttbar production, W+jets and Z+jets production, inclusive jet production and direct photon production will also be presented.
There have been recent updates to the three global PDF fits (CT, MSHT and NNPDF), all using significant amounts of data from the LHC, in addition to the non-LHC data sets that formed the core of previous iterations. Given the impact of the LHC data on the global PDF fits, and the impact that the new PDFs will have on physics comparisons at the LHC, it is crucial to perform a benchmarking among the PDFs and the predictions using these PDFs, similar in spirit to what was carried out for PDF4LHC15, widely used for LHC physics. The end result of this exercise will be a PDF4LHC21 set of PDFs, formed from the combination of the three global PDF sets. This talk will detail the benchmarking that has been performed, the similarities and differences observed, and the potential impact of the PDF4LHC21 PDFs on precision physics at the LHC.
Pre-recorded 3min talk with one-on-one discussion session via Gather Town
We explore a new energy regime, 5 TeV, for the diboson production in proton-proton collisions using 304/pb of data collected with the CMS detector. The diboson, WW, WZ, and ZZ, cross sections are measured analyzing events with two, three or four charged leptons in the final state. The cross sections are compared with NNLO predictions and across other experiments.
Measurements of multiple electroweak bosons production at the LHC constitutes a stringent test of the electroweak sector and provides 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 multi-boson production in proton-proton collisions at √s=13 TeV. The measurements exploit both the leptonic and hadronic decays of the weak vector bosons and in some cases the production in association with jets is explored. Differential cross sections are measured, which 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 in some cases are reinterpreted in terms of an effective field theory to constrain new physics beyond the Standard Model.
A measurement of the W+W- boson pair production cross section in proton-proton collisions at 13 TeV is presented. The data used in this study are collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 35.9 fb-1. The W+W- candidate events are selected by requiring two oppositely charged leptons (electrons or muons) aiming to measure the total production cross section, the fiducial cross sections, and the normalized differential cross sections within the fiducial region. Finally, a dilepton invariant mass distribution is used to probe for physics beyond the standard model in the context of an effective field theory, and constraints on the presence of dimension-6 operators are derived.
We will discuss the sensitivity to quartic anomalous couplings between photons and W/Z bosons at the LHC using intact protons in the final state. This allows obtaining a negligible background for 300 fb$^{-1}$ of data and improves the sensitivities to anomalous couplings by two or three orders of magnitude compared to standard methods. We will also discuss the sensitivity to axion-like particles that also improves by two orders of magnitude.
The scattering of electroweak bosons tests the gauge structure of the Standard Model and is sensitive to anomalous weak boson self interactions. In this talk, we present recent results on weak-boson fusion and weak-boson scattering from the ATLAS experiment using proton-proton collisions at √s=13 TeV. We present the first observation of ZZ production via weak-boson scattering as well as evidence for Z𝛾 production, in final states where the Z boson decays leptonically. This is augmented by a measurement of VV production via weak-boson scattering in semileptonic decay channels. Measurements of Vjj final states produced via weak-boson fusion will also be presented. If available, new results on weak-boson production will also be shown.
The ALICE experiment is upgraded for LHC Run 3 in order to profit from the increase in luminosity in particular for the heavy ion data taking with an expected interaction and readout rate of 50 kHz, and to improve on the tracking resolution. The upgrades comprise replacing the Inner Tracking System with a new silicon tracker using MAPS technology, including a new tracking system in the forward direction for the reconstruction of trajectories of charged particles from the primary vertex to the muon spectrometer. The readout of the upgraded TPC is based on GEM foils, to reduce ion backflow and allow for continuous data taking. A new fast interaction trigger will provide the collision trigger and serve as luminometer. In addition, several detectors have been equipped with faster readout. In order to fully exploit the potential of the new detectors, also the software framework has been adapted to the new conditions, providing a first pass reconstruction during the data taking process to compress the data. The upgrades will provide new opportunities e.g. for measurement of heavy-flavour hadrons, low-mass dileptons, quarkonia and jets with unpreceded precision, particularly in heavy-ion collisions. We present an overview of the status of the detector and software upgrades of the ALICE experiment in preparation for Run 3 and provide an outlook of the future of the ALICE experiments in later LHC runs, including a high-granularity electromagnetic and hadronic calorimeter in the forward direction (FOCAL) and further upgrades of the inner tracking system with new silicon sensor technology (ITS3).
The High-Luminosity Large Hadron Collider (HL-LHC) is expected to deliver up to 3000 fb-1 of proton-proton collisions at 14 TeV center-of-mass energy. The CMS detector will undergo significant upgrades for HL-LHC operations. We will present prospects for selected Standard Model and Higgs sector measurements with the CMS detector at the HL-LHC, and discuss potential sensitivity to several beyond-Standard Model new physics scenarios.