An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment

TL;DR

The paper addresses determining proton parton distribution functions (PDFs) and the strong coupling αs(MZ) using ZEUS data from HERA in a single, consistent NLO QCD framework. It combines inclusive deep inelastic scattering cross sections with jet production data, treating correlated systematics rigorously and using a sophisticated weight-based approach for NLO jet predictions. The results yield well-constrained valence, sea, and especially gluon PDFs, with a precise extraction of αs(MZ) that benefits from the jet data, illustrating clear QCD factorisation within one experiment. The study also shows compatibility with Tevatron jet data and demonstrates the feasibility of extracting fundamental QCD parameters from HERA data alone, with expectations for further improvements from future data.

Abstract

The ZEUS inclusive differential cross-section data from HERA, for charged and neutral current processes taken with e+ and e- beams, together with differential cross-section data on inclusive jet production in e+ p scattering and dijet production in γp scattering, have been used in a new NLO QCD analysis to extract the parton distribution functions of the proton. The input of jet data constrains the gluon and allows an accurate extraction of α_s(M_Z) at NLO; α_s(M_Z) = 0.1183 \pm 0.0028(exp.) \pm 0.0008(model) An additional uncertainty from the choice of scales is estimated as \pm 0.005. This is the first extraction of α_s(M_Z) from HERA data alone.

Figures (6)

• Figure 1: ZEUS-JETS fit compared to ZEUS low-$Q^2$$e^+ p$ NC reduced cross sections, $\tilde{\sigma}_{\rm NC}$.
• Figure 2: ZEUS-JETS fit compared to ZEUS high-$Q^2$ NC $e^+ p$ and $e^- p$ reduced cross sections, $\tilde{\sigma}_{\rm NC}$.
• Figure 3: ZEUS-JETS fit compared to ZEUS high-$Q^2$ CC $e^+ p$ and $e^- p$ reduced cross sections, $\tilde{\sigma}_{\rm CC}$.
• Figure 4: ZEUS-JETS fit compared to ZEUS DIS jet data. Each cross section has been multiplied by the scale factor in brackets to aid visibility.
• Figure 5: ZEUS-JETS fit compared to photoproduced dijet data. Each cross section has been multiplied by the scale factor in brackets to aid visibility.