Substructure dependence of jet cross sections at HERA and determination of alphas

TL;DR

This paper measures jet substructure and cross sections at HERA, using these data to test QCD predictions and determine the strong coupling constant alpha_s with high precision.

Contribution

It provides detailed measurements of jet substructure and cross sections, and extracts a precise value of alpha_s from jet shape data in ep scattering.

Findings

Jet shapes and subjet multiplicities agree with QCD calculations.

Jet cross sections follow expected parton dynamics.

Alpha_s(Mz) determined to be 0.1176 with uncertainties.

Abstract

Jet substructure and differential cross sections for jets produced in the photoproduction and deep inelastic ep scattering regimes have been measured with the ZEUS detector at HERA using an integrated luminosity of 82.2 pb-1. The substructure of jets has been studied in terms of the jet shape and subjet multiplicity for jets with transverse energies Et(jet) > 17 GeV. The data are well described by the QCD calculations. The jet shape and subjet multiplicity are used to tag gluon- and quark-initiated jets. Jet cross sections as functions of Et(jet), jet pseudorapidity, the jet-jet scattering angle, dijet invariant mass and the fraction of the photon energy carried by the dijet system are presented for gluon- and quark-tagged jets. The data exhibit the behaviour expected from the underlying parton dynamics. A value of alphas(Mz) of alphas(Mz) = 0.1176 +-0.0009(stat.) -0.0026 +0.0009 (exp.) -0.0072 +0.0091 (th.) was extracted from the measurements of jet shapes in deep inelastic scattering.