A phenomenological study of the final combined HERA data on inclusive
deep inelastic scattering (DIS) has been performed. The data are
presented and investigated for a kinematic range extending from
values of the four-momentum transfer of the exchanged boson, $Q^2$,
above $10^4$ GeV$^2$ down to the lowest values observable at HERA of
$Q^2$, and Bjorken $x_{\rm Bj}$ of $Q^2 = 0.045$ GeV$^2$...
The sensitivity of CMS measurements to Parton Distribution Functions, strong coupling constant and treatment of heavy flavours in QCD analyses is presented. CMS data collected at various center-of-mass energies and their impact on the PDFs are presented. Measurements of cross sections of jet and to-quark pair production are in particular sensitive to the gluon distribution in the proton and...
Over the past several years, parton distribution functions (PDFs) have become more precise. However there are still kinematic regions where more data are needed to help constrain global PDF extractions, such as the sea quark distributions $\bar{d}$/$\bar{u}$ near the valence region (Bjorken-x $\approx$ 0.1 - 0.3). Current measurements appear to suggest different high-x behaviors of these...
Precision measurements of the Drell-Yan production of W and Z bosons at the LHC provide a benchmark of our understanding of perturbative QCD and electroweak processes and probe the proton structure in a unique way.
The ATLAS collaboration performed a precision Z/gamma* measurement at a center of mass energy of 8 TeV in the di-lepton mass range up to the TeV scale. These are performed...
We present the recent progress on parton distribution functions (PDF) of the proton from the CTEQ-TEA collaboration.
I present a summary of the current status of MMHT PDFs. Recent updates include the effects of additional data from the LHC. The inclusion of new jet data and of the full NNLO corrections to the cross sections are studied. We also look at the implications from improved data on vector boson production and how these affect the quark flavour decomposition. Another focus is the inclusion of QED...
The exploitation of the exciting physics program of the Run II of the Large Hadron Collider requires high-precision theoretical calculations, of which the parton distribution functions (PDFs) of the proton are a central ingredient. In this talk we present the new update of the NNPDF family of global analysis, NNPDF3.1. This new PDF set is based on the NNPDF3.0 fitting framework supplemented...
We present results from the most recent global QCD analysis by the CTEQ-Jefferson Lab (CJ) Collaboration on the flavour content of the nucleon sea quark distributions. Constraints from LHC, Fermilab and Jefferson Lab data on the SU(2) flavour asymmetry, dbar - ubar, as well as on the strange asymmetry s - sbar will be discussed.
The APPLgrid and fastNLO projects provide a fast and flexible way to reproduce the results of perturbative QCD cross section calculations with any input PDF. The latest developments from these projects are presented, concentrating especially on the joint project (APPLfast), providing a common interface to state-of-the-art NNLO QCD calculations from NNLOJET. Additional features from new...
APFEL is a numerical code specialised for PDF fits that provides a fast and accurate solution of the DGLAP equations. In addition to PDF evolution, APFEL also provides a module for the computation of DIS cross sections in several mass schemes. In this contribution, I will present the most recent and relevant developments carried out in APFEL. They include: the computation of the time-like...
We have developed a new procedure to determine Parton Distribution Functions (PDFs) and their uncertainties, based on Markov Chain Monte Carlo
methods. We will show in this talk how we can replace the standard $\chi^2$ minimization by procedures grounded on Statistical Methods, and on Bayesian inference in particular, thus offering additional insight into the rich field of PDFs. The...
The workshop on Parton Distributions and Lattice Calculations in the LHC era (PDFLattice2017) has been hosted at Balliol College, Oxford (UK), shortly before DIS2017. The workshop has brought together communities involved in the determination of the parton distribution functions (PDFs) from lattice QCD, on the one hand, and from global QCD analyses of the data, on the other hand. The goal was...
While it is long known that the quark stature of the nucleon is modified in the nuclear medium, we still lack understanding of the underlying physical mechanism that causes this modification. Understanding this mechanism will teach us about the interplay between partonic and nucleonic degrees of freedom in nuclear systems and is therefore a main challenge of modern nuclear physics.
In this...
The proton-lead programme at CERN's Large Hadron Collider allowed the study of cold-nuclear matter effects from the initial state, such as Cronin enhancement, nuclear shadowing and gluon saturation. They result in a modification of the production cross section and thus provide crucial tests of predictions from perturbative Quantum-Chromodynamics. Furthermore, these control measurements are...
Nuclear parton distribution functions are essential to the understanding of proton-lead collisions. We will review several measurements from CMS that are particularly sensitive to nPDFs. W and Z bosons are medium-blind probes of the initial state of the collisions, and we will present the measurements of their production cross sections in pPb collisions at 5.02 TeV, and as well a asymmetries...
We have studied the prospects of using the Drell–Yan dilepton process in pion–nucleus collisions as a novel input in the global analysis of nuclear parton distribution functions (nPDFs). In a NLO QCD framework, we find the measured nuclear cross-section ratios from the NA3, NA10 and E615 experiments to be largely insensitive to the pion parton distributions and also compatible with the EPS09...
We report on EPPS16 - the first analysis of NLO nuclear PDFs where LHC p-Pb data (Z, W, dijets) have been directly used as a constraint. In comparison to our previous fit EPS09, also data from neutrino-nucleus deeply-inelastic scattering and pion-nucleus Drell-Yan process are now included. Much of the theory framework has also been updated from EPS09, including a consistent treatment of heavy...
We use nCTEQ15 nPDFs with uncertainties to identify measurements which
have a potential impact on nuclear corrections and flavor
differentiation. In particular, recent LHC W/Z vector boson
production data in proton-lead and lead-lead collisions are quite
sensitive to heavier flavors (especially the strange PDF). This
complements the information from neutrino-DIS data. As the proton
flavor...
We present the status of our calculation of nuclear parton distribution functions on the basis of our microscopic model, which takes into account a number of nuclear effects including nuclear shadowing, Fermi motion and nuclear binding, nuclear meson-exchange currents and off-shell corrections to bound nucleon distributions. We discuss a number of applications from Deep Inelastic Scattering to...
We present a quark-diquark model for nucleons where the light front wave functions are constructed form the soft-wall AdS/QCD prediction. The model is consistent with quark counting rule and Drell-Yan-West relation. The scale evolution of the PDFs are simulated by making parameters scale dependent. The model reproduces the scale evolution of unpolarized PDF for a wide range of energy scale...
Polarized semi-inclusive deep inelastic scattering (SIDIS) plays a crucial role in understanding sea quark contributions to the proton spin through global analyses of spin-dependent parton distribution functions (PDFs). The shape of the strange quark polarization in particular has been shown to be dramatically different between analyses that include or exclude SIDIS data. The inclusion of...
Abstract:
We discuss a solution of the DGLAP parton evolution equations,
written in terms of Sudakov form factors to describe the branching
and no-branching probabilities, with a Monte Carlo method. We
show explicitly numerically, that this method reproduces exactly
the semi-analytical solutions also at NLO.
We discuss numerical effects of the kinematic boundary of resolvable
branchings...
We present the impact of recent V+jets measurements performed by the CMS collaboration on the constraints of PDFs.
Realizing the precision physics paradigm at the LHC requires the calculation of hard-scattering cross-sections which include perturbative QCD corrections up to (N)NNLO and electroweak corrections up to NLO. For consistency, parton distribution functions (PDFs) need to be provided with matching accuracy, which in the case of QED effects involves introducing the photon parton distribution of the...
Novel tagged beam and target techniques are being developed to create effective neutron, pion, and other targets from nucleon and nuclear targets and beams. The effective meson targets in particular open the opportunity to uniquely probe the structure and composition of mesons and the nucleon sea. This talk will discuss some results from the 6 GeV era at Jefferson Lab, approved and possible...
Neutrino-nucleus charged-current deep inelastic scattering (DIS) provides a complementary probe to charged lepton-nucleus DIS in the study of nuclear and hadronic structure. The MINERvA experiment is a dedicated neutrino scattering experiment located on the NuMI beamline in Fermilab. With multiple nuclear targets of Pb, Fe, CH, and C in the same beam, MINERvA has the capability to add to the...
We have computed the fourth-order nf2 contributions to all three non-singlet quark–quark splitting functions and their four nf3 flavour-singlet counterparts for the evolution of the parton distributions of hadrons in perturbative QCD with nf effectively massless quark flavours. In this talk we give an overview of the method used to reconstruct the analytic form of these functions from their...
The combined inclusive DIS data from HERA are described
with DGLAP fits at NLO and NNLO, combined with a model
for twist 4 corrections originating from the GBW saturation
model. Besides the higher twist effects, modifications
are introduced at small x to the input functions for the
twist 2 parton distribution functions that are inspired by
findings of QCD at high parton densities. It is shown...
We present CT14 Monte-Carlo replica PDFs that reproduce important properties of CT14 Hessian PDFs: the asymmetry of CT14 uncertainties and positivity of individual parton distributions. The ensembles of CT14 Monte-Carlo replicas constructed this way at NNLO and NLO are suitable for various collider applications, such as cross section reweighting.
We present the xFitter project (former HERAFitter) which provides a unique open-source software framework for the determination of the proton's PDFs and for the interpretation of the physics analyses in the context of Quantum Chromodynamics.
We highlight the new xFitter software release which includes state-of-the-art theoretical developments with direct applications for the various PDF...
Current (and future) collider energies, as well as high-energy astroparticle interactions in the atmosphere, allow to probe the proton at very small values of the parton momentum fraction x. At small x, both perturbative partonic coefficients and DGLAP splitting functions are affected by a logarithmic growth, which eventually spoils the perturbativity of the alphas expansion. These small-x...
The strange-quark parton distribution function (PDF) is difficult to extract from global fits since there is little available data with good sensitivity to the strange quarks, particularly at large x. Knowledge of the strange quark PDF is an important part of a wholistic understanding of the nucleon. Assumptions about the shape of the distribution are made based on the up and down quark sea,...
The APPLgrid and fastNLO projects provide a fast and flexible way to reproduce the results of perturbative QCD cross section calculations with any input PDF. The latest developments from these projects are presented, concentrating especially on the joint project (APPLfast), providing a common interface to state-of-the-art NNLO QCD calculations from NNLOJET. Additional features from new...
The fastNLO framework allows to efficiently re-evaluate very
time-consuming higher-order calculations in perturbative QCD
for different choices of the strong coupling constant and evolution,
parton distribution functions, or renormalisation and factorisation scales.
Originally, this technique was developed to permit the inclusion of
next-to-leading order jet cross sections into fits of...
