Inclusive-jet photoproduction at HERA and determination of alphas

TL;DR

This paper reports measurements of inclusive-jet cross sections in ep collisions at HERA, compares them with QCD predictions, and extracts the strong coupling constant alpha_s(Mz) with high precision.

Contribution

It provides detailed measurements of jet cross sections using multiple algorithms and determines alpha_s(Mz) from HERA data, enhancing precision in QCD tests.

Findings

QCD calculations generally agree with measurements except at low ETjet and high etajet.

Measured ratios of different jet algorithms match theoretical predictions including up to O(alpha_s^2).

Extracted alpha_s(Mz) value is 0.1206 with competitive experimental and theoretical uncertainties.

Abstract

Inclusive-jet cross sections have been measured in the reaction ep->e+jet+X for photon virtuality Q2 < 1 GeV2 and gamma-p centre-of-mass energies in the region 142 < W(gamma-p) < 293 GeV with the ZEUS detector at HERA using an integrated luminosity of 300 pb-1. Jets were identified using the kT, anti-kT or SIScone jet algorithms in the laboratory frame. Single-differential cross sections are presented as functions of the jet transverse energy, ETjet, and pseudorapidity, etajet, for jets with ETjet > 17 GeV and -1 < etajet < 2.5. In addition, measurements of double-differential inclusive-jet cross sections are presented as functions of ETjet in different regions of etajet. Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low ETjet and high etajet. The influence of non-perturbative effects not related to hadronisation was studied. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O(alphas2) terms. Values of alphas(Mz) were extracted from the measurements and the energy-scale dependence of the coupling was determined. The value of alphas(Mz) extracted from the measurements based on the kT jet algorithm is alphas(Mz) = 0.1206 +0.0023 -0.0022 (exp.) +0.0042 -0.0035 (th.); the results from the anti-kT and SIScone algorithms are compatible with this value and have a similar precision.