Combination of measurements of inclusive deep inelastic $${e^{\pm }p}$$ e ± p scattering cross sections and QCD analysis of HERA data

Abstract

This paper is dedicated to the memory of Professor Guido Altarelli who sadly passed away as it went to press. The results which it presents are founded on the principles and the formalism which he developed in his pioneering theoretical work on Quantum Chromodynamics in deep-inelastic lepton-nucleon scattering nearly four decades ago rent e ± p scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb −1 and span six orders of magnitude in negative four-momentum-transfer squared, Q 2 , and Bjorken x. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixedflavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in α s (M 2 Z ) = 0.1183 ± 0.0009(exp) ± 0.0005(model/parameterisation) ± 0.0012(hadronisation) and results on electroweak unification and scaling violations are also presented. H1 and ZEUS

Collinear and TMD quark and gluon densities from parton branching solution of QCD evolution equations

“…In figure 5 the calculated cross section σ red , obtained from the fit using xFitter, is compared with the precision measurements from HERA [61] for different values of Q 2 , showing very good agreement from low to high values of Q 2 .…”

“…Further we present the results of fits, based on this approach, to the high-precision DIS data [61]. First results from this work have appeared in [62,63].…”

“…We compare collinear parton density functions obtained by our partonbranching solution with results obtained via the evolution package Qcdnum [64][65][66]. In section 4 we illustrate an application of our method by performing a fit to the high-precision DIS data [61]. For the fit we use an updated version of the program [67] within the xFitter open-source QCD fit platform [68].…”

“…A general tool to perform such fits to collider measurements is the xFitter package [68]. As an application of our formalism, in this section we describe the method and results of a fit to the precision DIS data [61].…”

“…(4.1) can be then used within the xFitter package to calculate the cross sections and to determine the parameters of the starting distributions A 0,b (x). We use precision measurements, in neutral-current and charged-current interactions at various beam energies from HERA 1+2 [61], of the reduced cross section…”