Scaling violations and determination of alpha(s) from jet production in gamma p interactions at HERA

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, E_T^jet, for jets with E_T^jet > 17 GeV and pseudorapidity -1 < eta^jet < 2.5, in the gamma-p centre-of-mass-energy range 142 < W_gamma-p < 293 GeV. Scaled jet invariant cross sections are presented as a function of the dimensionless variable x_T = 2 E_T^jet/W_gamma-p for = 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 values shows clear non-scaling behaviour. A value for the strong coupling constant of alpha_s(M_Z) = 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/dE_T^jet. The variation of alpha_s with E_T^jet is in good agreement with the running of alpha_s as predicted by QCD.

Note:

28 pages, 4 figures, 3 tables, submitted to Phys. Lett. B Report-no: DESY-02-228

electron p: colliding beams
electron p: inclusive reaction
jet: photoproduction
differential cross section: transverse energy
rapidity dependence
quantum chromodynamics: perturbation theory
scaling: violation
strong interaction: coupling constant
ZEUS
experimental results

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