Abstract
A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current $e^{\pm}p$ 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 fixed-flavour-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 $\alpha_s(M_Z)=0.1183 \pm 0.0009 {\rm(exp)} \pm 0.0005{\rm (model/parameterisation)} \pm 0.0012{\rm (hadronisation)} ^{+0.0037}_{-0.0030}{\rm (scale)}$. An extraction of $xF_3^{\gamma Z}$ and results on electroweak unification and scaling violations are also presented.
Highlights
Deep inelastic scattering (DIS) o√f electrons1 on protons at centre-of-mass energies of up to s 320 GeV at HERA has been central to the exploration of proton structure and quark–gluon dynamics as described by perturbative Quantum Chromo Dynamics [1]
The set of parton distribution functions (PDFs) denoted as HERAPDF1.0 [2] was based on the combination of all inclusive DIS scattering cross sections obtained from HERA I data
It follows from Eq 1 that the structure function x F3 can be determined from the difference between the e+ p and e− p reduced cross sections: x F3
Summary
Deep inelastic scattering (DIS) o√f electrons on protons at centre-of-mass energies of up to s 320 GeV at HERA has been central to the exploration of proton structure and quark–gluon dynamics as described by perturbative Quantum Chromo Dynamics (pQCD) [1]. The paper presented here is based on the combination of all published H1 [3,4,5,6,7,8,9,10] and ZEUS [11,12,13,14,15,16,17,18,19,20,21,22,23,24] measurements from both HERA I and II on inclusive DIS in NC and CC reactions This includes data taken with proton beam energie√s of E p = 920, 820, 575 and 460 GeV corresponding to s 320, 300, 251 and 225 GeV. The set of PDFs denoted as HERAPDF1.0 [2] was based on the combination of all inclusive DIS scattering cross sections obtained from HERA I data.
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