Conveners
Structure function and parton densities: Parallel Sessions 1
- Katarzyna Wichmann (DESY, Hamburg)
Structure function and parton densities: Parallel Sessions 2
- Maria Zurita (University of Regensburg)
Structure function and parton densities: Parallel Sessions 3
- Benjamin Nachman
Structure function and parton densities: Parallel Sessions 3
- Maria Zurita (University of Regensburg)
Structure function and parton densities: Parallel Sessions 4
- Katarzyna Wichmann (DESY, Hamburg)
Structure function and parton densities: Parallel Sessions 5
- Benjamin Nachman
Structure function and parton densities: Parallel Sessions 5
- Maria Zurita (University of Regensburg)
Structure function and parton densities
- Katarzyna Wichmann (DESY, Hamburg)
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,...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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....
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...
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...
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...
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...
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...
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...
Measurements of deep inelastic scattering on the deuteron with detection of the spectator nucleon in the final state (spectator tagging) represent a unique method for extracting the free nucleon structure functions and studying the nuclear modifications of bound nucleons. The detection of the spectator nucleon (with typical momenta $\sim$ 100 MeV/c in the deuteron rest frame) fixes the nuclear...
Jets provide one of the primary tools to study the partons inside
protons. The cross section of inclusive jet production is one of the
main observables to study the hard scattering. It is well described by
pQCD in the collinear factorization framework. For proton-proton
collisions at RHIC at a center-of-mass energy $\sqrt{s} =
200~\text{GeV}$, the STAR detector provides measurements at...
Comprehensive measurements of differential cross-sections of top-quark-antiquark pair-production are presented. The measurements are performed in the dilepon, lepton+jets and the all-hadronic channels which allow for reconstruction of the top-quark and top-quark-pair kinematic distributions. The two channels are complementary in terms of range and resolution for several variables, including...
Deeply Virtual Compton Scattering (DVCS) is the golden exclusive reaction to study Generalized Parton Distributions (GPDs). Such exclusive measurements were performed at COMPASS in 2016 and 2017 at the M2 beamline of the CERN SPS using the 160 GeV muon beam scattering off a 2.5m long liquid hydrogen target surrounded by a barrel-shaped time-of-flight system to detect the recoiling target...
Naively, the amounts of $\bar{d}$ and $\bar{u}$ in the proton were expected to be the same based on the flavor-independence of the strong coupling.
However, the muon deep inelastic scattering experiment NMC at CERN found $\bar{d}>\bar{u}$ in the proton.
Drell--Yan experiments also obtained the results consistent with it.
The Drell--Yan experiment E866 at Fermilab showed that...
The factorization of the differential cross section Drell-Yan and DIS has recently allowed several extractions oof TMD. The extractions are based on the double-evolution of TMD and a matching on PDF. The new results show a high sensitivity to the PDF sets that I like too discuss in this talk and that can be interesting for future analyses. Several recent results obtained by our group will be shown.
The Parton Branching (PB) approach provides a way to obtain transverse momentum dependent (TMD) parton densities. Its equations are written in terms of splitting functions and Sudakov form factors and can be solved with Monte Carlo methods. Even though the transverse momentum is known in every branching, the PB method currently uses the DGLAP splitting functions, which assume that the parton...
We present the first determination of transverse momentum dependent (TMD) photon densities with the Parton Branching (PB) method. The photon distribution is generated perturbatively without intrinsic photon component. The input parameters for quarks and gluons are determined from fits to precision measurements of deep inelastic scattering (DIS) cross sections at HERA. The TMD densities are...
We perform a quantitative study of different methods used to solve evolution equations in QCD ($\alpha_s$, PDFs, TMDs).
We highlight differences and similarities between numerical and analytical solutions, focusing on the $q_T$ spectrum of Drell-Yan pair production analysed in the context of TMD/SCET-factorisation vs. qT-resummation formalism.
The final aim is to provide a reliable...
I shall discuss phenomenological consequences of merging the proper QCD Sudakov
resummation with small-$x$ effects, which allows us to compute gluon
distributions that depend on longitudinal momentum, transverse momentum and the
hard scale of the process. The small-$x$ resummation is included by means of the
BK equation supplemented with a kinematic constraint and subleading...
We investigate the so-called Lorentz invariance relations from the standpoint of the proper definitions of
partonic correlations functions resulting from factorization; that is
in light the proper treatment of ultraviolet divergences. We show that there are corrections to the naive Lorentz invariance relations are nontrivial even in very simple renormalizable quantum field theories. We...
While the unpolarized valence quark ($d$ and $u$) distributions are well determined from DIS experiments, the sea quark counterparts, $\bar{d}$ and $\bar{u}$, are much less constrained, in particular, near the valence region. Measurements of $W^+/W^-$ production ratio in $pp$ collider experiments, such as the STAR experiment at RHIC, are sensitive to the $\bar{d}/\bar{u}$ ratio at leading...
Recently, jet measurements in DIS events close to Born kinematics have been proposed as a new probe to study transverse-momentum-dependent (TMD) PDFs, TMD fragmentation functions, and TMD evolution. We report measurements of lepton-jet momentum imbalance and hadron-in-jet correlations in high-Q2 DIS events collected with the H1 detector at HERA. The jets are reconstructed with the kT algorithm...
In the context of the Transverse-Momentum-Dependent (TMD) description of the nucleon structure, it is important to study the distributions of the transverse-momentum squared $P_T^2$ and the amplitudes of the azimuthal modulations (azimuthal asymmetries) of charged hadrons produced in Semi-Inclusive DIS. The $P_T^2$ - distributions and the azimuthal asymmetries can be related to the intrinsic...
The differential cross section measurements of the production of a pair of opposite-charged leptons as a function of pt and phi* in various bins of its invariant mass M are presented. The results are obtained using proton-proton collision data recorded with the CMS detector at the LHC. Measurements are also compared to state-of-the-art generators as well as TMD based predictions.
Following our recent Monte Carlo determination of the pion’s PDFs from Drell-Yan (DY) and leading neutron electroproduction data from the Jefferson Lab Angular Momentum (JAM) collaboration, we extend the analysis by including effects from threshold resummation. At higher orders in the strong coupling, $\alpha_S$, soft gluon emissions cause large logarithmic corrections, which become important...
I will report on an ongoing effort towards calculating the N4LO perturbative QCD corrections to the DIS total inclusive cross-section. We are developing a method based on differential equations and series expansion in the inverse Bjorken parameter. As a byproduct our calculation should also deliver analytic or at least precise numerical approximations for the four-loop splitting functions.
Measurements of jet production in proton-proton collisions at the LHC are crucial for precise tests of QCD, improving the understanding of the proton structure and are important tool for searches for physics beyond the standard model. We present recent measurements of double-differential cross section of jet production at centre-of-mass energy of 13 TeV with 2016 data and compare them to...
We present the status for the measurement of cross sections of weak boson production as a function of the boson's kinematics, by the STAR experiment at RHIC. Results combine data from unpolarized p+p collisions at $\sqrt{s}$ = 500 and 510 GeV collected during the 2011, 2012, 2013, and 2017 runs, corresponding to an integrated luminosity of 700 pb$^{-1}$. The differential $Z^{0}$ cross section,...
