Scaling violations and determination of alphas from jet production in gamma-p interactions at HERA
Abstract
Differential cross sections for jet photoproduction in the reaction ep --> e jet X have been measured with the ZEUS detector at HERA using 82.2 pb-1 of integrated luminosity. Inclusive jet cross sections are presented as a function of the jet transverse energy, ETjet, for jets with ETjet > 17 GeV and pseudorapidity -1 < etajet < 2.5, in the gamma-p centre-of-mass-energy range 142 < Wgamma-p < 293 GeV. Scaled jet invariant cross sections are presented as a function of the dimensionless variable xT = 2 ETjet/Wgamma-p for <Wgamma-p> = 180 and 255 GeV. Next-to-leading-order QCD calculations give a good description of the measured differential cross sections in both magnitude and shape. The ratio of scaled jet invariant cross sections at the two <Wgamma-p> values shows clear non-scaling behaviour. A value for the strong coupling constant of alphas(MZ) = 0.1224 +- 0.0001 (stat.) + 0.0022 - 0.0019 (exp.) + 0.0054 - 0.0042 (th.) has been extracted from a QCD analysis of the measured dsigma/dETjet. The variation of alphas with ETjet is in good agreement with the running of alphas as predicted by QCD.
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