Conveners
WG 1: Structure Functions and Parton Densities 1
- Aurore Courtoy (IFPA)
- Aurore Courtoy (Instituto de Física, UNAM)
- Claire Gwenlan (University of Oxford (GB))
- Simone Amoroso (Deutsches Elektronen-Synchrotron (DE))
WG 1: Structure Functions and Parton Densities 2
- Aurore Courtoy (Instituto de Física, UNAM)
- Simone Amoroso (Deutsches Elektronen-Synchrotron (DE))
- Aurore Courtoy (IFPA)
- Claire Gwenlan (University of Oxford (GB))
WG 1: Uncertainties
- There are no conveners in this block
WG 1: Structure Functions and Parton Densities 4
- Claire Gwenlan (University of Oxford (GB))
- Simone Amoroso (Deutsches Elektronen-Synchrotron (DE))
- Aurore Courtoy (IFPA)
- Aurore Courtoy (Instituto de Física, UNAM)
WG 1: Lattice and Precision (theory)
- There are no conveners in this block
We report the results of a new global QCD analysis including deep-inelastic scattering (DIS) data off $^1$H, $^2$H, $^3$H, and $^3$He targets. Nuclear corrections are treated in terms of a nuclear convolution approach with off-shell bound nucleons. The off-shell corrections responsible for the modification of the structure functions (SFs) of bound nucleons are constrained in a global fit along...
In relativistic heavy ion collisions, the charged ions produce an intense flux of equivalent photons. Thus, photon-induced processes are the dominant interaction mechanism when the colliding nuclei have a transverse separation larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs), the photon provides a clean, energetic probe of the partonic structure of the nucleus,...
Analyzing data from nuclear lepton Deep-Inelastic Scattering, Drell-Yan processes, and W and Z boson production, we show that factorizing nuclear structure into quasi-free nucleons and universally modified close-proximity Short Range Correlated (SRC) nucleon pairs allows us to fully describe the quark-gluon structure of nuclei down to very-low momentum fractions. This is the first combined...
Motivated by the wide range of kinematics covered by current and planned DIS facilities, we revisit the formalism, practical implementation, and numerical impact of target mass corrections (TMCs) for DIS on nuclear targets. These corrections are especially crucial for EIC physics. Within the Operator Product Expansion (OPE) formalism, we extend the analysis from individual nucleon targets...
We consider the extension of the MSHT20 PDFs to an approximate N$^3$LO order. We describe the parameterisation of the missing N$^3$LO contributions and the determination of the theoretical uncertainties and their interpretation. We examine the impact of further data sets and look at the stability of predicted cross sections.
Measurements of Deep Inelastic Scattering (DIS) provide a powerful tool to probe fundamental structure of protons and other nuclei. The DIS cross sections can be expressed in terms of structure functions which are conventionally constructed via parton distribution functions (PDFs) that obey the DGLAP evolution equations. However, it is also possible to formulate the DGLAP evolution directly in...
Parton distribution functions (PDFs) are most commonly determined by parameterizing them at some input scale Q_0 and then evolved to the desired scale Q through the DGLAP evolution equations. Extensions of the DGLAP equations have been proposed to account not only for the splitting of partons but also including non-linear 1/Q^n terms from the recombination of partons which slows down the pace...
In the parton branching (PB) approach, Collinear and TMD parton densities have been determined by fits to inclusive deep inelastic scattering (DIS) HERA data. This method allows one to simultaneously take into account soft-gluon emission and the transverse momentum recoils in the parton branchings along the QCD cascade. The latter leads to a natural determination of the TMD PDFs in a proton. A...
We present recent progress within the NNPDF analysis of parton distribution functions aimed to i) improve the accuracy of the determination by accounting for (approximate) N3LO corrections to the splitting functions and partonic matrix elements, ii) estimate the impact of missing higher order uncertainties within the NNLO global analysis, and iii) account for QED corrections and the impact of...
We provide a summary of recent developments on the MSHT parton distribution functions. This includes the addition of a variety of new data sets into the fit, and the potential impact of EIC data. The primary impact is seen on the details of the high-$x$ PDFs. We also consider the impact of procedural choices, and the effect of changes of PDFs on predicted cross sections.
We discuss recent developments in the global QCD analysis of parton distribution functions by CTEQ-TEA collaboration.
The question of the existence and possible magnitude of nonperturbative (often called "intrinsic") charm in the proton has long confounded attempts to cleanly isolate such a contribution in global analyses of high-energy experiments. In this talk, we show that the available (non)perturbative QCD theory and hadronic data have still not developed to a sufficient level to clearly resolve this...
We report about the impact of novel high-precision top-quark pair production 13 TeV measurements and other HF data from ATLAS and CMS on the CT18 global analysis of PDFs. We discuss features of a new top-quark data combination which complements the CT18 baseline. We discuss the impact on the gluon PDF and the extraction of the mass of the top quark in the pole mass approximation.
This...
We present the xFitter project which provides an open-source software framework for the determination of the proton's parton distribution functions and for the interpretation of the physics analyses in the context of Quantum Chromodynamics. The project has been used for a number of analyses performed by the LHC collaborations and theory community, which are summarised briefly. The xFitter...
A new measurement of inclusive jet cross sections in neutral current deep inelastic scattering using the ZEUS detector at the HERA collider is obtained. The data were taken at HERA 2 at a center of mass energy of 318 GeV and correspond to an integrated luminosity of 347 pb−1. Massless jets, reconstructed using the kT-algorithm in the Breit reference frame, are measured as a function of the...
Recent measurements of jet cross sections in proton-proton collisions with the CMS experiment are presented. The measured jet cross sections are corrected for detector effects and compared with the predictions from perturbative QCD, and exploited to derive constraints on parton distribution functions and to mesure alpha_S.
SeaQuest has measured dimuon events from the interaction of 120 GeV proton beam on liquid hydrogen and deuterium targets with dimuon mass between 2 and 8 GeV. These dimuon events contain both the Drell-Yan process and the charmonium ($J/\psi$ and $\psi^\prime$) production. The first result of the Drell-Yan $(p+d)/2(p+p)$ cross section ratio, based on the analysis of a fraction of the collected...
While the unpolarized valence quark ($d$ and $u$) distributions are well determined from DIS and $pp/p\bar{p}$ experiments, their 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 $\bar{d}/\bar{u}$...
Presented are the latest updates of the measurement of the azimuthal decorrelation angle and the transverse momentum imbalance between the leading jet and the scattered lepton in deep inelastic scattering with the ZEUS detector at HERA. During the HERA II data-taking period, electrons and positrons collided with protons with a center of mass energy of 318 GeV. The total integrated luminosity...
Correlations between charged particles provide important insight about the hadronization process. The analysis of the momentum difference between charged hadrons in pp, p-lead, and lead-lead collisions of various energies is performed in order to study the dynamics of hadron formation. The spectra of correlated hadron chains are explored and compared to the predictions based on the quantized...
We review various methods used to estimate uncertainties in quantum correlation functions, such as parton distribution functions (PDFs). Using a toy model of a PDF, we compare the uncertainty estimates yielded by the traditional Hessian and data resampling methods, as well as from explicitly Bayesian analyses using nested sampling or hybrid Markov chain Monte Carlo techniques. We investigate...
Precise and accurate parton distributions are necessary to reach the physics goals of future colliders, from search for new physics to claims on non-perturbative QCD. In the last years, the CT group has expanded the concept of uncertainties in PDF analyses, in particular by including the concept of “sampling accuracy” in contrast to “fitting accuracy.” The exploration of the sampling accuracy...
We present a methodology to improve the determination of PDF parametrization, the Fantômas4QCD package. It is achieved through Bézier curve fitting. Thanks to the implementation of our technique in the xFitter package, we have performed a global analysis of the pion PDF — the first analysis to account for the role of the functional form in its uncertainty.
When performing fits to data using the popular $\chi^2$ approach, uncertainty to fit parameters is determined by contours of $\Delta\chi^2=T^2$, where the tolerance $T =1 $ corresponds to the $68\%$ confidence level. PDF fits have to deal with the problem of having data sets, particularly from different experiments, that are in tension with each other. The traditional approach used by PDF...
Electron scattering data off protons from the CLAS12 detector in Hall B at Jefferson Laboratory have become available and cover a wide kinematic range in W up to 2.5 GeV and Q2 up to 9 GeV2, offering new opportunities to explore inclusive, semi-inclusive, and fully exclusive reactions. A study that aims to extract the inclusive electroproduction cross sections from the CLAS12 data collected at...
Charge symmetry of the nucleon has been critically important in understanding the partonic structure of nuclei because halves the number of quark PDFs -- $u^p(x) = d^n(x)$ and $u^n(x) = d^p(x)$. Going back to the charge independence of the nuclear force, this symmetry is well founded, however, there are known sources of charge symmetry violation (CSV) such as the quark masses and...
An important physics program at the JLAB12 and EIC facilities is understanding the emergence of the masses and internal structures of Goldstone mesons, pion and kaon, through measurements of their electromagnetic form factors at large momenta transfers, $Q$. In this talk we will present first results of pion and kaon electromagnetic form factors up to $Q^2=10$ GeV$^2$ and $Q^2=30$ GeV$^2$,...
abstract attached
The high-x data from the ZEUS Collaboration are used to extract parton density distributions of the proton deep in the perturbative regime of QCD. The data primarily constrain the up-quark valence distribution and new results are presented on its x-dependence as well as on the momentum carried by the up-quark. The results were obtained using Bayesian analysis methods which can serve as a...
We discuss the preliminary results of the new global nCTEQ23 nuclear PDF analysis, combining a number of our previous analyses into one consistent framework with updates to the underlying theoretical treatment as well as the addition of new available data. In particular, the nCTEQ23 global release will be the first nCTEQ release containing neutrino DIS scattering data in a consistent manner...
We present the new CJ22 global QCD analysis of unpolarized parton distributions The work focuses on the light antiquark sea to incorporate constraints from recent SeaQuest and STAR electroweak boson production data. We make use of a more flexible antiquark imbalance parametrization than in the CJ15 analysis, that in turn is sensitive to mid-rapidity correlations between the $\bar d / \bar u$...
Extractions of the structure functions from inclusive h(e,e′) and d(e, e′) reactions are important for the study of nucleon structure. Such extractions help with constraining the PDF (specially at large Bjorken X), facilitate the studies of Quark Hadron Duality and are important for non-singlet moments calculation as a test of LQCD and many more. Experiment E12-10-002 ran in Hall C at JLab in...
The precision-level reached at collider experiments offer us the unique opportunity to probe the inner structure of the protons and heavy nuclei, described in the language of parton density functions (PDFs), at an unprecedented accuracy. Despite that current determination of the proton PDFs account for nuclear effects and reciprocally the determination of the nuclear PDFs (nPDFs) depend on the...
The structure of hadrons relevant for deep-inelastic scattering are completely characterised by the Compton amplitude. A direct calculation of the Compton amplitude provides a complementary way to accessing the structure functions, circumventing the operator mixing and renormalisation issues of the standard operator product expansion approach.
In this talk, we focus on the QCDSF/UKQCD...
Studying the structure of Nucleons in Quantum Chromodynamics is a challenging task due to the appearance of non-perturbative Parton Distribution Functions (PDF).
PDFs describe the distributions of quarks and gluons with respect to the longitudinal momentum and appear in cross-sections as process-independent contributions.
Lattice QCD provides the possibility to study these by calculating...
We present the first physical-continuum limit $x$-dependent nucleon gluon distribution from lattice QCD using the pseudo-PDF approach, on lattice ensembles with $2+1+1$ flavors of highly improved staggered quarks (HISQ), generated by MILC Collaboration. We use clover fermions for the valence action on three lattice spacings $a \approx 0.9$, 0.12 and 0.15~fm and three pion masses $M_\pi \approx...
Parton distribution functions (PDFs) are defined from matrix elements of operators separated along the light cone, which cannot be determined directly from calculations performed in Euclidean space. Despite this, various approaches for extracting information on PDFs from lattice QCD have been developed, all of which involve a factorization of the lattice QCD computed matrix element with...
We present a lattice QCD calculation of the unpolarized isovector quark parton distribution function (PDF) of the proton utilizing a perturbative matching at next-to-next-leading-order (NNLO). The calculations are carried out using a single ensemble of gauge configurations generated with $N_f$ = 2+1 highly improved staggered quarks with physical masses and a lattice spacing of a =0.076 fm. We...
The fact that lattice QCD is defined in a finite-Euclidean spacetime, prohibits direct access of inclusive scattering observables from lattice QCD. In principle, one can envision determining such quantities from real-time computations, such as those that may be eventually performed using quantum computers. Looking forward into the future, in this talk I outline a possible pathway towards...
Factorization theorems have long been a successful and elegant tool to describe and interpret hadronic structure. The early parton model picture, first developed by Feynman, has now been generalized past the leading power description of inclusive processes like deep inelastic scattering (DIS) to semi-inclusive ones like SIDIS and much more. However, a consistent description of both collinear...
The splitting functions determine the scaling violations of deep-inelastic scattering structure functions and govern the evolution of Parton densities. A determination of N3LO Parton densities requires the knowledge of 4-loop splitting functions. It is important to find efficient methods to compute 4-loop splitting functions. The method of computing the off-shell matrix elements with a...
In this talk we discuss on recent result on massless and massive Wilson
coefficients in the polarized and unpolarized case up to 3-loop order.
This includes the gluonic massive operator matrix element $A_{gg}$
which enters the definition of the Variable-Falvor-Number-Scheme, and the
calculation of the unpolarized and polarized massless Wilson coefficients.
While the calculation of the...
We have calculated the $n_f^2$ and $n_f^3$ contributions to the flavour non-singlet structure functions $F_2$ and $F_L$ in inclusive deep-inelastic scattering at the fourth order in the strong coupling $\alpha_s$. The coefficient functions have been obtained by computing a very large number of Mellin-N moments using the method of differential equations, and then determining the analytic forms...
The factorization theorem plays an important role in the analysis of high energy quantum chromodynamic (QCD) processes, separating the nonperturbative hadronic interaction into the universal parton distribution functions (PDFs) and fragmentation functions (FFs) and the process-dependent interactions into short distance perturbative calculations, with any interference power suppressed. With a...
With the recent computation of cross-section calculations up to the third order in perturbative QCD, and the appearance of the first PDF fits at N3LO (albeit only approximately), it becomes interesting to study if the improved precision is accompanied by an analogue improvement in accuracy in describing experimental data.
To this aim, we calculated the theoretical total cross-sections for...
