We present the first open-source analysis of parton distribution functions (PDFs) of charged pions using xFitter, an open-source QCD fit framework to facilitate PDF extraction and analyses. Our calculations are implemented at next-to-leading order (NLO) using APPLgrids generated by the MCFM generator. Using currently available Drell-Yan and photon production data, we find the valence distribution is well constrained; however, the considered data are not sensitive enough to unambiguously determine sea and gluon distributions. Fractions of momentum carried by the valence, sea and gluon components are discussed, and we compare with the results of the JAM collaboration and the GRV group.

Fits to the final combined HERA deep-inelastic scattering cross-section data within the conventional DGLAP framework of QCD have shown some tension at low x and low . A resolution of this tension incorporating -resummation terms into the HERAPDF fits is investigated using the xFitter program. The kinematic region where this resummation is important is delineated. Such high-energy resummation not only gives a better description of the data, particularly of the longitudinal structure function , it also results in a gluon PDF which is steeply rising at low x for low scales, , contrary to the fixed-order NLO and NNLO gluon PDF.

Non-perturbative QCD effects from Parton Distribution Functions (PDFs) may be constrained by using high-statistics Large Hadron Collider (LHC) data. Drell-Yan (DY) measurements in the Charged Current (CC) case provide one of the primary means to do this, in the form of the lepton charge asymmetry. We investigate here the impact of measurements in Neutral Current (NC) DY data mapped onto the Forward-Backward Asymmetry (A FB ) on PDF determinations, by using the open source fit platform xFitter. We demonstrate the potential impact of A FB data on PDF determinations and perform a thorough analysis of related uncertainties.

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We study charm production in charged-current deep-inelastic scattering (DIS) using the xFitter framework. Recent results from the LHC have focused renewed attention on the determination of the strange-quark parton distribution function (PDF), and the DIS charm process provides important complementary constraints on this quantity. We examine the current PDF uncertainty and use LHeC pseudodata to estimate the potential improvement from this proposed facility. As xFitter implements both fixed-flavorand variable-flavor-number schemes, we can compare the impact of these different theoretical choices; this highlights some interesting aspects of multi-scale calculations. We find that the high-statistics LHeC data covering a wide kinematic range could substantially reduce the strange PDF uncertainty.

In this work, a new set of parton distribution functions taking into account the intrinsic charm (IC) contribution is presented. We focus on the impact of the EMC measurements on the large x charm structure function as the strongest evidence for the intrinsic charm when combined with the HERA, SLAC and BCDMS data. The main goal of this paper is the simultaneous determination of the intrinsic charm probability P cc/p and strong coupling αs. This allows us to study the interaction of these two quantities as well as the influence on the PDFs in the presence of IC contributions. By considering αs which can be fix or free parameter from our QCD analysis, we find that although there is not a significant change in the extracted central value of PDFs and their uncertainties, the obtained value of P cc/p change by factor 7.8%. The extracted value of P cc/p in the present QCD analysis is consistent with the recent reported upper limit of 1.93%, which is obtained for the first time from LHC measurements. We show the intrinsic charm probability is sensitive to the strong coupling constant and also the charm mass. The extracted value of the strong coupling constant αs(M 2 Z ) = 0.1191 ± 0.0008 at NLO is in good agreement with world average value and available theoretical models.

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