Conveners
WG1: Structure Functions and Parton Densities: Session 1
- Thomas Cridge (University College London)
- Klaus Rabbertz (KIT - Karlsruhe Institute of Technology (DE))
- Barak Schmookler (Stony Brook University)
WG1: Structure Functions and Parton Densities: Session 2
- Klaus Rabbertz (KIT - Karlsruhe Institute of Technology (DE))
- Thomas Cridge (University College London)
- Barak Schmookler (Stony Brook University)
WG1: Structure Functions and Parton Densities: Session 3
- Thomas Cridge (University College London)
- Barak Schmookler (Stony Brook University)
- Klaus Rabbertz (KIT - Karlsruhe Institute of Technology (DE))
In this talk we present the NNPDF4.0 global analysis. As compared to its predecessor, NNPDF3.1, the new NNPDF4.0 fit includes 44 new datasets, mostly from the LHC, benefits from a novel machine learning methodology based on hyperparameter optimisation and stochastic gradient descent, is based on state-of-the-art NNLO QCD calculations, and accounts for NLO electroweak corrections and nuclear...
MSHT20 is the latest PDF fit from the MRST/MSTW/MMHT/MSHT collaboration, representing our most accurate and precise determination of the PDFs to date it is designed for the LHC precision era. We present a general review and outline further progress which has been made. This includes the effects of varying the strong coupling α_S (M_Z^2) and the masses of the charm and bottom quarks. We...
We discuss recent developments in the global QCD analysis of parton distribution functions by CTEQ-TEA collaboration.
Motivated by recent progress in the PDF determinations carried out by the CT, MSHT, and NNPDF groups, we present an updated combination of global PDF fits: PDF4LHC21. It is based on the Monte Carlo combination of the CT18, MSHT20, and NNPDF3.1 sets followed by either its Hessian reduction or its replica compression. Extensive benchmark studies are carried out in order to disentangle the origin...
The HERAPDF2.0 ensemble of parton distribution functions (PDFs) was introduced in 2015. The final stage is presented, a next-to-next-to-leading-order (NNLO) analysis of the HERA data on inclusive deep inelastic $ep$ scattering together with jet data as published by the H1 and ZEUS collaborations. A perturbative QCD fit, simultaneously of $\alpha_S(M_Z^2)$ and and the PDFs, was performed with...
Recent progress in global analyses have led to pressing questions about precision and accuracy. NNLO PDFs must balance between the precision of experimental constraints and robustness (stability) with respect to the choice of experimental sets and methodological assumptions. We critically compare various strategies for achieving this balance in the Hessian and Monte Carlo formalisms adopted by...
We present a QCD analysis of Drell-Yan W and Z cross-sections using a wide range of measurements from the RHIC, Tevatron and LHC colliders, together with the Deep Inelastic Scattering data from the HERA-2 collider. The study is performed using the xFitter framework and employs a consistent set of theoretical predictions at NNLO in QCD and NLO in EW couplings. Predictions using modern PDFs are...
We present the MCscales approach for incorporating scale uncertainties in parton
distribution functions. The method builds on the Monte Carlo sampling method
for propagating experimental uncertainties to PDFs that underlies the NNPDF
approach, by extending it to the space of factorisation and renomalisation
scales for the processes entering a PDF fit. A prior probability is assigned...
We present a general formalism for the inclusion of theoretical uncertainties from missing higher orders into a parton distribution function (PDF) fit. We demonstrate how using the currently available knowledge about the next-to-next-to-next-to-leading order (N$^3$LO), an order above the standard NNLO used in current PDF fits, can provide consistent, justifiable and explainable estimates for...
Almost all PDF fits so far take into account experimental uncertainties but not the uncertainties on theoretical predictions. Because theoretical predictions are typically computed at finite order in perturbation theory, they suffer from (often sizeable) uncertainties due to the missing higher orders. In a recent NNPDF study, theory uncertainties evaluated using scale variation have been...
Gluon nuclear Parton distribution functions (nPDFs) have been the subject of many studies over the past years, since they are important for many processes and difficult to constrain. Recently, nCTEQ15 nPDFs have been updated with vector boson and single inclusive hadron production data to address this issue. To constrain the gluon nPDF further, particularly towards $x$ values smaller than...
We present a systematical study on proton-PDF uncertainties in the extraction of nuclear PDFs from W$^\pm$ production data in proton-lead collisions, using the theoretical covariance matrix and Hessian PDF reweighting methods to quantify the impact. We then discuss different ways to mitigate these theoretical uncertainties, including self-normalization, forward-to-backward and nuclear...
Nuclear parton distribution functions (nPDFs) quantify the initial-state nuclear effects and provide a factorization-based input for perturbative calculations in nuclear collisions. These distributions can be determined in a global QCD analysis using wide range of experimental data. In addition to older fixed-target deep inelastic scattering and Drell-Yan dilepton production data, several...
We present an updated determination of nuclear parton distributions (nPDFs) from a global NLO QCD analysis of hard processes in fixed-target lepton-nucleus and proton-nucleus together with collider proton-nucleus experiments. In addition to neutral- and charged-current deep-inelastic and Drell-Yan measurements on nuclear targets, we consider the information provided by the production of...
We report the results of a new global QCD analysis which includes deep-inelastic $e/\mu$ scattering (DIS) data off proton and deuterium, as well as lepton pair production in Drell-Yan process in $pp$ and $pD$ collisions and $W^\pm/Z$ boson production data from $pp$ and $p \bar p$ collisions at LHC and Tevatron. We address nuclear corrections in DIS in terms of a nuclear convolution model with...
We construct a new parametrization of nuclear PDFs (nPDFs) inspired by short-range correlation (SRC) models, and implement this in a global fit. The SRC motivated parametrization decomposes the nPDFs into a free nucleon component, and a part describing the formation of the bound nucleon pairs. Here, the A-dependence enters only through multiplicative factors describing the number of the...
We perform the first global QCD analysis of pion valence, sea quark, and gluon distributions within a Bayesian Monte Carlo framework with threshold resummation on Drell-Yan cross sections at next-to-leading logarithmic accuracy. Exploring various treatments of resummation including in Mellin-Fourier and double Mellin space, we find that the behavior of the valence quark distribution at...
Missing higher order uncertainties (MHOU) in perturbative computations are usually estimated by varying the unphysical scales present in the process. However, it is known that scale variation prescriptions often underestimate the actual uncertainty. In this talk, we present a more reliable approach to approximate the unknown next-to-next-to-leading order (NNLO) transverse momentum distribution...
The QCD strong coupling (alpha_s) and the parton distribution functions (PDFs) of the proton are fundamental ingredients for phenomenology at high-energy facilities such as the Large Hadron Collider (LHC).
It is therefore of crucial importance to estimate any theoretical uncertainties associated to them.
Both alpha_s and PDFs obey their own renormalisation-group equations (RGEs) whose...
We will report on recent works featuring the parton distribution functions (DFs) of pion-like systems at experimental scales, following an approach based on the assumption that there is an effective charge which defines an evolution scheme for DFs that is all-orders exact. Within this framework, strict lower and upper bounds on all Mellin moments of the valence-quark DFs are derived....
Transverse-momentum-dependent parton distribution functions (TMD PDFs) are essential for describing elementary high-energy processes involving the hadron, such as semi-inclusive deep-inelastic scattering (SIDIS). Basis Light-Front Quantization (BLFQ) now provides the hadron's light-front wave functions in the leading Fock sector of three valence quarks. We report the first calculations within...
Transverse momentum dependent (TMD) distributions match collinear parton density functions (PDF) in the limit of small transverse distances, which is accounted for by global extractions of TMD distributions. We study the influence of the PDF choice on the determination of unpolarized TMDPDFs and the description of TMD Drell-Yan-pair and Z-boson production data. We find that PDF essentially...
Parton branching solutions of QCD evolution equations have recently been studied
to construct both collinear and transverse momentum dependent (TMD) Parton
distributions. In this formalism, soft-gluon colour coherence effects are taken into account by
introducing the soft-gluon resolution scale. In this talk, we show results of fits to the high precision deep inelastic scattering (DIS)...
With transverse-momentum-dependent parton densities (TMD) obtained from fits to HERA DIS data using the Parton Branching (PB) method, we determine the non-perturbative Collins-Soper (CS) kernel. The CS kernel describes the rapidity evolution of quark TMD parton distribution functions. We use PB-TMD calculations of the Drell-Yan (DY) transverse momentum spectrum at different DY masses. We show...
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...
With the detector instrumented in the forward region, the collected Z boson events in the LHCb acceptance can be used to probe the proton structure. In this talk, the latest Z boson related measurements will be presented: the Z boson production cross-section measurement at 13 TeV, the Z boson angular coefficients measurement, and the measurement of Z+ c jet events for probing intrinsic charm....
We present fits to determine parton distribution functions (PDFs) using a diverse set of measurements from the ATLAS experiment at the LHC, including inclusive W and Z boson production, ttbar production, W+jets and Z+jets production, inclusive jet production and direct photon production. These ATLAS measurements are used in combination with deep-inelastic scattering data from HERA. Particular...
The CMS measurements of double-differential inclusive jet cross sections of and triple-differential top quark-antiquark pair production cross sections at the center of mass energy of 13 TeV are used together with the data of inclusive deep inelastic scattering to extract the parton distribution functions in the proton, the top quark mass and the strong coupling constant. Using standard model...
A first measurement of the 1-jettiness event shape observable in neutral-current deep-inelastic electron-proton scattering is presented. The 1-jettiness observable $\tau_{1b}$ is defined such that it is equivalent to the thrust observable defined in the Breit frame. The data were taken in the years 2003 to 2007 with the H1 detector at the HERA ep collider at a center-of-mass energy of 319 GeV...
The EMC effect -- the modification of quarks in bound nucleons -- is a decades-old open question in QCD research, with far-reaching implications for our understanding of the fundamental structure of matter. While inclusive deep inelastic scattering (DIS) measurements have characterized many features of the EMC effect, their insensitivity to the initial state of the struck bound nucleon limits...
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. Unlike the Drell-Yan process which probes the antiquark distributions in the nucleons, the charmonium production is...
The cross section for inclusive jet production in high-energy $pp$ collisions is well described by pQCD in the collinear factorization framework, which, together with its high rate and clear signal, makes it a key observable to study the proton structure. For $pp$ collisions at RHIC at a center-of-mass energy of $\sqrt{s} = 200~\text{GeV}$, the STAR detector provides jet measurements at $0.07...
While the unpolarized valence quark ($d$ and $u$) distributions are well determined from DIS 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 $\bar{d}/\bar{u}$ ratio at leading...
We perform a global QCD analysis of unpolarized parton distributions within a Bayesian Monte Carlo framework, including the new $W$-lepton production data from the STAR Collaboration at RHIC and Drell-Yan di-muon data from the SeaQuest experiment at Fermilab. We assess the impact of these two new measurements on the light antiquark sea in the proton, and the $\bar{d}-\bar{u}$ asymmetry in...
We present a new approach to fitting the $e^+P$ and $e^-P$ high-$x$ data from the ZEUS experiment\footnote{H.~Abramowicz et al. (ZEUS Collaboration), Phys. Rev. D
89, 072007 (2014); I.~Abt et al. (ZEUS Collaboration), Phys.Rev.D 101 (2020) 11, 112009 } based on a full forward modeling from the input PDFs to the expected number of events in measurement bins. Systematic uncertainties are...
We present a novel method to reconstruct the kinematics of neutral-current deep inelastic scattering (DIS) using a deep neural network (DNN). Unlike traditional methods, it exploits the full kinematic information of both the scattered electron and the hadronic-final state, and it accounts for QED radiation by identifying events with radiated photons and event-level momentum imbalance. The...
We present EKO, a new PDF evolution code, and yadism, a new DIS structure function library. Both programs produce operators which are independent from the boundary condition, can be stored and quickly applied to several PDFs.As a first application we show a determination of intrinsic charm content of the proton. Both codes are fully open source and written in Python, with a modular structure...
In this talk, the xFitter project is presented. xFitter is an open-source package that provides a framework for the determination of the parton distribution and fragmentation functions for many different kinds of analyses in Quantum Chromodynamics (QCD). xFitter version 2.2.0 has recently been released and offers an expanded set of tools and options. xFitter has been used for a number of...
Fast interpolation-grid frameworks facilitate an efficient and flexible evaluation of higher-order predictions for any choice of parton distribution functions (PDFs) or value of the strong coupling constant $\alpha_s$. They constitute an essential tool for the extraction of PDFs and Standard Model parameters as well as studies of the dependence on the renormalization and factorization scales....
The Drell-Yan lepton pair productions have been measured to an unprecedented precision level at the LHC. In companion, the theoretical calculations should reach the same level. However, a visible discrepancy among different next-to-next-to-leading order (NNLO) calculations has been discovered by both the CTEQ-TEA group and also by S. Alekhin et al. In this study, we carefully examine the...
We present a new methodology that is able to yield a simultaneous deter- mination of the Parton Distribution Functions (PDFs) of the proton alongside any set of parameters that determine the theory predictions; whether within the Standard Model (SM) or beyond it. The SIMUnet methodology is based on an extension of the NNPDF4.0 neural network architecture, which allows the addition of an extra...
Recently, the $Q^2$ dependence of several low moments of the proton longitudinal structure function, $F_L$, has been mapped thanks to the measurements taken at HERA and JLAB. In this contribution, we present the first lattice QCD determination of the lowest moment of $F_L$ and its $Q^2$ dependence. This is achieved by computing the forward Compton amplitude via an application of the...
There have been rapid developments in direct lattice-QCD calculations of the Bjorken-x dependence of parton distributions. In this talk, I will highlight selected recent lattice-QCD results on parton distributions with emphasis on calculations at physical pion mass when applicable. Results include the continuum-physical isovector nucleon PDF, a first study of the strange and charm PDFs, the...
The light-cone definition of Parton Distribution Functions (PDFs) does not allow for a direct ab initio determination employing methods of Lattice QCD simulations that naturally take place in Euclidean spacetime. In this presentation we focus on pseudo-PDFs where the starting point is the equal time hadronic matrix element with the quark and anti-quark fields separated by a finite distance. We...
Recent reduced pseudo Ioffe time distributions and matrix elements of current-current correlators generated from lattice QCD are used simultaneously with experimental data to extract pion parton distribution functions (PDFs) from a Monte Carlo global QCD analysis. Through the complementarity of the experimental and lattice QCD data, the analysis rigorously quantifies both the uncertainties of...
In this contribution, I will present a novel dynamical model for the pion based on the solution of the Bethe-Salpeter equation in Minkowski space. Our approach considers the pion as a bound state of a pair quark anti-quark interacting through the one-gluon exchange. The inputs of the model are the quark and gluon masses, and a scale parameter related to the extended quark-gluon vertex. Within...
We obtain the light meson light-front wavefunctions (LFWFs) from the light-front QCD Hamiltonian, determined for their constituent quark-antiquark and quark-antiquark-gluon Fock components, together with a three-dimensional confinement. By fitting the model parameters to achieve the light-meson mass spectroscpy, the LFWFs provide a good quality description of the pion electromagnetic form...
We describe the phenomenological implications of a new heavy-quark mass scheme, called the Physical Scheme, that accounts for the effects of intrinsic heavy-quarks and provides a way to smoothly transition over the heavy-quark thresholds. We will present results for the DIS coefficient functions for $F_2$ and $F_L$ at NLO in the Physical Scheme showing that they reduce to the familiar...
Heavy flavor mass effects are significant in deep inelastic scattering (DIS) processes, and their systematic treatment becomes of more importance as we approach a one-percent accuracy in the determination of Parton Distribution Functions (PDFs). These effects are included through so-called variable flavor number schemes (VFNS), and most of the ingredients that are required by these schemes...
The anomalous dimensions of local quark and gluon operators determine the
scaling violations of the deep–inelastic scattering structure functions
and are therefore instrumental in the measurement of the strong coupling constant
and the evolution of the parton densities.
In this talk I present our recalculation of the 2- and 3-loop
anomalous dimensions with the traditional method of...
The computation of the structure functions for DIS can be tested across a range of energies with high accuracy and provides vital information for the evolution in the distribution of partons within a proton. We are currently investigating DIS at 4-loop, in particular the non-singlet sector.
Our approach consists of the determination large number of Mellin Moments, allowing for the...
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 nuclear matter. The experiment incorporates full azimuth vertexing, tracking, and a complete set of electromagnetic and hadronic calorimeters over the pseudorapidity range |η| < 1.1. This powerful...
It has been argued for more than four decades that the proton could have a sizeable intrinsic component of the lightest heavy quark, the charm quark. Innumerable efforts to establish intrinsic charm in the proton have remained inconclusive. In this talk we present evidence for intrinsic charm by exploiting a high-precision determination of the quark-gluon content of the nucleon based on the...
Study of parton distribution functions (PDFs) has led to a better understanding of the partonic structure of hadrons and the proton structure function in deep inelastic scattering. Knowledge of parton densities within the hadrons is vital to predict the hard-scattering process results. Owing to theoretical and experimental limitations, PDFs cannot be computed from first principles. The global...
We present a Leading-Order PDFs fitting within the CT18 framework, i.e., CT18 LO PDFs. To improve the fitting results, we imposed two treatments: 1) exclude 5 data sets, which cannot be correctly described with LO QCD theory, from the CT18 global data set; 2) apply a K-factor to mimic the NLO QCD corrections to Drell-Yan processes. The strong coupling as input for CT18 LO is fixed to be its...
We present a Leading-Order PDFs fitting within the CT18 framework, i.e., CT18 LO PDFs. To improve the fitting results, we imposed two treatments: 1) exclude 5 data sets, which cannot be correctly described with LO QCD theory, from the CT18 global data set; 2) apply a K-factor to mimic the NLO QCD corrections to Drell-Yan processes. The strong coupling as input for CT18 LO is fixed to be its...
In this work, we investigate the dependence of proton $k_t$-factorization structure functions on the different sets of parton distribution functions (PDFs), i.e. MMHT2014, CJ15lo, CTEQ6l1, HERAPDF15, MSTW2008 and MSHT20. The Kimber-Martin-Ryskin (KMR) unintegrated parton distribution functions (UPDFs), which can use the above PDFs sets as input, are considered to calculate the
proton...
Hard Exclusive Meson Production (HEMP) and Deeply Virtual Compton Scattering (DVCS) are very promising reactions to access 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 2.5 m long liquid hydrogen target surrounded by a barrel-shaped time-of-flight...
The large-momentum effective theory (LaMET) is a systematic approach to calculate parton physics from Euclidean approaches such as lattice QCD. In this talk, I will present a state-of-the-art lattice QCD calculation of pion valence quark distribution with the hybrid scheme and the first-time implementation of next-to-next-to-leading order LaMET matching correction, which is done using two fine...
Modern analysis on parton distribution functions (PDFs) requires calculations of the log-likelihood functions from thousands of experimental data points, and scans of multi-dimensional parameter space with tens of degrees of freedom. In conventional analysis the Hessian method has been widely used to approximate profile of the log-likelihood functions in neighborhood of the best-fit, and to...
We present a systematic quantum algorithm, which integrates both the hadronic state preparation and the evaluation of the real-time light-front correlations, to study the parton distribution functions (PDFs). As a proof-of-concept, we realize the first direct simulation of the PDFs in the 1+1 dimensional Nambu-Jona-Lasinio model. We show the results obtained by numerical diagonalization and by...
We present a new determination of unpolarised charged pion and kaon fragmentation functions from a set of single-inclusive electron-positron annihilation and lepton-nucleon semi-inclusive deep-inelastic scattering data. The determination includes next-to-next-to-leading order QCD corrections to both processes, and is carried out in a framework that combines a neural network parametrisation of...
We discuss a method to study free protons and neutrons using $\nu(\bar \nu)$-hydrogen (H) Charged Current (CC) inelastic interactions using $\nu$ and $\bar \nu$ CC interactions on both H and nuclear targets. Probing free nucleons with (anti)neutrinos provides information about their internal structure, as well as a crucial input for the modeling of $\nu(\bar \nu)$-nucleus (A) interactions....
One of the primary physics goals of the future electron-ion collider (EIC) is understanding the origin of nucleon spin from measurements of polarized DIS and SIDIS. Current analyses suggest that approximately 40% of nucleon spin is carried by gluon spin, and 30% each carried by quark spin and orbital angular momentum. However, existing data only extends to $x \approx 0.01$, and...
The potential of the future Electron Ion Collider to constrain proton and nuclear collinear parton densities is explored using data simulated in the context of the proposed ATHENA detector. For the proton, projections relative to a `DIS-only’ approach are obtained in the HERAPDF2.0 framework. Substantial improvements in precision are observed at large x for valence quark, sea quark and gluon...
Motivated by the approval of the Electron-Ion Collider, we report the status of modeling electron-ion scattering at NLO in QCD with the general-purpose simulation framework MadGraph5_aMC@NLO.
We investigate the strangeonia and strange mesons system in Basis Light-front Quantization(BLFQ) approach. We adopt a light-front effective Hamiltonian with transverse and longitudinal light-front holography confining potential. The effective Hamiltonian is retaining up to the first two Fock sector therefore we can contain one gluon dynamics in the meson system. This work is based on our light...
Semi-inclusive deep-inelastic scattering (SIDIS) is among the key observables at the future Electron-Ion Collider. This talk will present performance studies of the proposed ATHENA detector (A Totally Hermetic Electron-Nucleus Apparatus) for key observables in SIDIS. In particular we present studies of observables sensitive to the Sivers effect, unpolarized transverse momentum dependent parton...
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 nuclear matter. The experiment incorporates full azimuth vertexing, tracking, and a complete set of electromagnetic and hadronic calorimeters over the pseudorapidity range |η| < 1.1. This powerful...
Here, we present the extraction of the Parton Distribution Functions (PDFs) at
low x and at the next-to-leading order (NLO) approximation.
We show that the "sea quark distribution functions" have self-similar behavior or the "Fractal" behavior with fixed exponent at $x<0.01$. To this end, a simple parametrization for the sea quarks PDFs based on the "Fractal" approach is considered....
Recently data on W + D meson and W + c-jet production have started to be included in some PDF fits, mainly because of their potential for constraining the strange quark PDFs.
In this poster we present predictions for W + D-meson and W + c-jet production with NLO QCD accuracy matched with parton shower. We show how including the latter effects is fundamental in order to provide consistent...
