NNLO predictions for jet production in Deep Inelastic Scattering have recently become available. These are used to extend the QCD HERAPDF2.0Jets fits, that were made to extract PDFs from inclusive HERA data and HERA jet data, from NLO to NNLO. In addition new jet data sets have become available since the publication of HERAPDF2.0 and these are also considered.
We discuss the updates to the MMHT2014 PDFs. These are due to inclusion of ever-increasing amounts of LHC data, and simultaneously the treatment of more cross sections fully at NNLO. We also present the final results of our inclusion of QED effects in parton distributions.
We present the new CTEQ-TEA global analysis of Quantum Chromodynamics (QCD). In this analysis, parton distribution functions (PDFs) of the nucleon are determined within the Hessian method at the next-to-next-to-leading order (NNLO) in perturbative QCD, based on the most recent measurements from the Large Hadron Collider (LHC) and a variety of world experimental collider data. Next-to-leading...
A significant limitation in current PDF determinations is that the impact of theoretical uncertainties is not systematically accounted for. I will present a framework for the inclusion of additional sources of theoretical uncertainty in PDF fits, and present the first study of the effects of Missing Higher Order Uncertainties, which are estimated using scale variations, on PDFs in the context...
We report an update of the NNLO ABMP16 PDFs aimed to include recent
data on the Drell-Yan process, single- and pair-production of the top
quarks at the LHC, and the heavy-quark semi-inclusive DIS production with a
main focus on the small-x PDFs. The parameters of QCD Lagrangian,
strong coupling constants and the heavy quark masses, are determined
simultaneously with the PDFs and interplay...
Since the first measurements by the EMC that triggered the so-called “proton spin crisis”, many experimental programs have been carried out to understand the spin of the nucleon in terms of its partonic degrees of freedom. It is still today an active research area in QCD phenomenology, with ongoing programs at COMPASS, RHIC and Jefferson Lab measuring spin observables to be analyzed within a...
We present a first determination of the nuclear parton distribution functions (nPDF) based on the NNPDF methodology: nNNPDF1.0. This nPDF analysis is based on neutral-current deep-inelastic structure function data, and is performed using NNLO QCD calculations with heavy quark mass effects. For the first time in the NNPDF fits, the $\chi^2$ minimisation is carried out using stochastic gradient...
Parton distribution functions (PDFs) are important quantities that characterize the structure of hadrons at high energy. Calculating them from first principles have been a long standing challenge in hadron physics and particle physics. In the past few years, rapid progress has been made in directly computing PDFs from lattice QCD. In this talk, I will summarize the current status of lattice...
We present a PDF interpretation of events containing a vector boson produced in association with jets at a proton-proton collider, performed using ATLAS data from 2012 at a centre-of-mass energy of 8 TeV, together with ATLAS data on inclusive vector boson production at 7 TeV. The results are given relative to the ATLASepWZ16 PDF set, with consequences for the strangeness content of the sea....
Global QCD analyses of PDFs and fragmentation functions (FFs) have traditionally been performed in completely independent studies. The JAM Collaboration, in contrast, has embarked on a systematic program to simultaneously extract PDFs and FFs from a wide range of processes using Monte Carlo methods. In this talk I will report new results on spin-averaged and spin-dependent PDFs and FFs from a...
We consider impact of the large-log resummation emerging at the large momentum transfer $Q$ in the variable-flavour-number (VFN) scheme description when it is applied to analysis of the semi-inclusive DIS production of the charm and bottom quarks. Matching of the VFN scheme with the fixed-flavour-number (FFN) one at small $Q$ is also discussed and phenomenological relevance of these two...
We show how theoretical uncertainties due to nuclear effects may be
incorporated into global fits of proton parton distribution functions (PDFs)
that include deep-inelastic scattering and Drell-Yan data on
nuclear targets. We specifically consider the CHORUS, NuTeV and E605 data
included in the NNPDF3.1 fit, which used Pb, Fe and Cu targets, respectively.
We show that the additional...
We present an investigation of the theoretical uncertainties in parton distribution functions (PDFs) due to missing higher-order corrections in the perturbative predictions used in the fit, and their relationship to the uncertainties in subsequent predictions made using the PDFs. We consider in particular the standard approach of factorization and renormalization scale variation, and derive...
We study the threshold corrections for inclusive deep-inelastic scattering and resummation to N4LL accuracy. Using the form factor at four loops in the large-nc limit we are able to derive the soft-virtual coefficients at the four loops in large-nc approximation. We have presented the expression for resummation coefficients B4q coefficient for quarks which enters first time in the resummed...
E-906/SeaQuest is a fixed-target experiment at Fermilab designed to measure the flavor dependence of the light-quark sea in nucleons at high Bjorken-x. Previous experiments have shown a surprising drop of the $\bar{d}/\bar{u}$ ratio at high Bjorken-x and SeaQuest was designed to extend the measurement to higher Bjorken-x with a 120 GeV proton beam. The Drell-Yan process is used as a probe of...
In this contribution I will present the latest developments concerning the APFEL++ program. APFEL++ is a C++ rewriting of the Fortran 77 evolution code APFEL, it is based on a completely new code design and guarantees a better performance along with an optimal memory management. This makes APFEL++ suitable for a wide range of tasks: from the solution of the DGLAP evolution equations to the...
A brief review of developments for APPLgrid to allow PDF fits other than to the proton, or other non standard proton fits is presented. These include changes to allow fitting of the photon density within the proton, and changes to facilitate the use of distinct PDF sets for each of the incoming hadrons in hadron-hadron interactions.
We present recent results from the xFitter project--an open-source
software framework for the determination of PDFs and the analysis of
QCD physics. xFitter has been used for a variety of LHC studies
including the measurement of the strange PDF, which we briefly
summarize. Additionally, charged current DIS charm production
provides a complementary perspective on s(x). We make use of...
The sheer volume of the LHC experimental data sensitive to the hadronic structure presents a formidable challenge for the global QCD analysis. In the CT18 global analysis, we implemented new approaches to streamline identification of the LHC experiments that have the greatest promise for constraining parton distributions in the nucleon at the next-to-next-to-leading order accuracy. Toward this...
Fast interpolation grid technology provides a fast and flexible way to reproduce the results of perturbative QCD cross section calculations with any input PDF, choice of scales, or strong coupling. Recent developments in the APPLfast interface between the NNLOJET QCD calculation with both APPLgid and fastNLO are reported including the release of development versions of grids for QCD cross...
We present an efficient numerical solution of the DGLAP equations for single and double parton distribution functions (PDFs and DPDs), based on the Chebyshev interpolation of these functions.
For PDF evolution, our method allows for a higher numerical accuracy using a considerably smaller number of grid points compared to other methods. The DPD evolution is realized using an affordable...
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 ratio of the sea quark distributions $\bar{d}$/$\bar{u}$ near the valence region. Furthermore, current measurements appear to suggest different high-$x$ behaviors of this ratio. The...
We consider a new parametrisation for the parton distribution functions (PDFs) that is more flexible in the small-$x$ region. We implement it in the $\texttt{xFitter}$ open-source PDF fitting tool, and compare it to the default xFitter parametrization, widely used for many PDF studies, and notably for the HERAPDF determination. We find that we can describe the combined inclusive HERA I+II data...
Fracture functions are parton distributions of a hadron in the presence of an almost collinear particle observed in the final state. They are important ingredients in QCD factorization for processes where a particle is produced diffractively. Different kinds of fracture functions are used for a process in different kinematic regions depending on the scale of the momentum transfer. We take the...
In perturbative QCD, the masses of the hadrons involved in high energy reactions can usually be neglected. However, in the case of production of Kaons in electron-proton collisions at low (and not so low) beam energies this may not be a good approximation. In particular, a recent proposal to include hadron masses in theoretical calculations shows how these Hadron Mass Corrections can explain a...
We present recent developments in the theoretical description of
processes leading to the production of heavy flavours, which, together
with the most recent experimental data, are of interest for further
constraining present fits of Parton Distribution Functions. We compare
different approaches, and, for selected cases, we show the impact of
using the MSbar scheme as an alternative to the...
We present a fit to determine parton distribution functions (PDFs) using inclusive W± and Z/γ∗ boson and top-antitop production measurements from ATLAS in combination with deep-inelastic scattering data from HERA. The ATLAS W and Z boson data exhibit sensitivity to the valence quark distributions and the light quark sea composition, whereas the top-quark pair production data have sensitivity...
Detailed studies have been carried out on the impact of top pair production data from the LHC on the gluon PDF, in the context of the CTEQ-TEA global PDF fit. The data includes single differential distributions from ATLAS at and double differential distributions from CMS, both at 8 TeV. The relative impact of different physical observables related to top quark production was considered. All...
Differential measurements of top quark pair (tt) and single top quark (t-channel) production cross sections are presented using data collected by CMS. The cross sections are measured as a function of various kinematic observables of the top quarks and the jets and leptons of the event final state. The results are confronted with precise theory calculations. For the first time,...
We discuss the production of $W^+ W^-$ pairs and $t \bar t$ quark-antiquark pairs in proton-proton collisions induced by two-photon fusion including, for a first time, transverse momenta of incoming photons. The unintegrated inelastic fluxes (related to proton dissociation) of photons are calculated based on modern parametrizations of deep inelastic structure functions in a broad range of $x$...
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, renormalisation or factorisation scale, and different values for the strong coupling constant. Recent developments in the generation of fast interpolation grids using the DIS process with the NNLOJET generator through the standardised...
Charm production in charged current deep inelastic scattering has been measured for the first time in $e^\pm p$ collisions, using data collected with the ZEUS detector at HERA, corresponding to an integrated luminosity of 358 pb$^{−1}$. Results are presented separately for $e^+ p$ and $e^− p$ scattering at a centre-of-mass energy of $\sqrt{s} = 318$ GeV within a kinematic phase-space region of...
Jet measurements play an essential role in PDF fits and the available measurements will be briefly summarized. The primary experimental uncertainties in these measurements are the knowledge of the jet energy scale and resolution. The analyses used to evaluate these uncertainties will be described and how they are combined to form the set of uncertainties that dominate these measurements. How...
The production of prompt isolated photons at hadron colliders provides stringent tests of perturbative QCD and can be used to evaluate probability density functions of partons in the proton. In this talk, we present the measurements of the isolated-photon plus two jets and the inclusive isolated-photons cross sections, both measured using proton-proton collision data collected by the ATLAS...
Precision measurements of the production cross sections of W and Z bosons in proton-proton collisions provide stringent tests of perturbative QCD and yield important information about the parton distribution functions (PDFs) for quarks within the proton. We report measurements of fiducial integrated and differential cross sections for inclusive W+, W− and Z boson production, analysed in the...
In the last years the LHCb experiment established itself as an important contributor to heavy ion physics by exploiting some of its specific features.
Production of particles, notably heavy flavour states, can be studied in p-p, p-Pb and Pb-Pb collisions at LHC energies in the forward rapidity region (pseudorapidity between 2 and 5), providing measurements which are highly complementary to...
In this talk, a new QCD analysis for nuclear parton distribution functions (nPDFs) at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) will be presented. The framework of the analysis, including the form of the parametrisation as well as the included DIS datasets, will be discussed. The results of this QCD analysis will be compared to the existing nPDF sets and to the...
We quantify the impact of LHCb D-meson measurements at $\sqrt{s}=5\,{\rm TeV}$ on the EPPS16 and nCTEQ15 nuclear PDFs. In our study, the theoretical description of D-meson production is based on the recently developed SACOT-$m_{\rm T}$ variant of the general-mass variable-flavour-number formalism, and the impact on PDFs is estimated via profiling methods. We pay a special attention on the...
The CJ (CTEQ-Jefferson Lab) collaboration provides a global fit of parton distribution functions with a special emphasis on the large $x$ region. The latest CJ15 global analysis implemented deuteron nuclear corrections at the parton level, and included data that were sensitive specifically to the neutron. These nuclear corrections allow for a calculation of the $F_2$ structure functions of the...
Extraction of the strange quark PDF is a long standing puzzle. We use
nCTEQ nPDFs with uncertainties to examine W/Z production at the LHC
and try to study both the nuclear corrections and the flavor
differentiation. This complements the information from neutrino-DIS
data. Additionally, we look ahead to future facilities such as EIC,
LHeC, and LHC upgrades and use a new tool, PDFSense, to...
Theory uncertainty from missing higher orders is usually estimated using scale variation. While scale variation is certainly a good tool to guess the size of the next perturbative order, it lacks of a statistical (probabilistic) interpretation and it often underestimates the actual uncertainty. Having a statistical definition of theory uncertainties is not only need for a fair comparison with...
The knowledge of the proton parton densities for large $x$ is very important in the search for new physics signals at the LHC. For Bjorken-$x$ larger than 0.6 they are however poorly constrained by the data used in extracting the proton parton density functions (PDFs) and different pdf sets have large uncertainties, and differ considerably, in this regime. We compare the pdf sets most widely...
We present a new determination of Transverse Momentum Dependent (TMD)
parton distributions applying the Parton Branching method. The PB TMDs are
obtained from fits to precision DIS data using DGLAP splitting functions at
leading and higher order. In addition the CCFM splitting function will be applied
to include small x effects.
Applications of these new TMD distributions will be discussed.
We study the effects of angular ordering constraint on collinear and transverse momentum dependent (TMD) parton distributions functions (PDFs) obtained within the Parton Branching (PB) method. We compare it with virtuality and pt ordering definitions. We study the effect of ordering choice on predictions for Z boson pt spectrum, especially at low pt and we demonstrate the advantage of the...
Measurements of the forward-backward asymmetry in neutral-current Drell-Yan di-lepton production have primarily been used for determinations of the weak mixing angle $\theta_W$.
We investigate the possibility of using the reconstructed forward-backward asymmetry to place constraints on the determination of the parton distribution functions (PDFs). We perform this study using the open-source...
We present measurements of differential jet cross sections over a wide range in transverse momenta from inclusive jets to multi-jet final states. Studies on the impact that these measurements have on the determination of the strong coupling alpha_s as well as on parton density functions are reported.
