Inclusive-jet photoproduction at HERA and determination of αsαs

Inclusive-jet cross sections have been measured in the reaction ep→e+jet+Xep→e+jet+X for photon virtuality Q2<1 GeV2Q2<1 GeV2 and γp   centre-of-mass energies in the region 14217 GeV and −1<ηjet<2.5−1<ηjet<2.5. In addition, measurements of double-differential inclusive-jet cross sections are presented as functions of ETjet in different regions of ηjetηjet. Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low ETjet and high ηjetηjet. 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(αs2) terms. Values of αs(MZ)αs(MZ) were extracted from the measurements and the energy-scale dependence of the coupling was determined. The value of αs(MZ)αs(MZ) extracted from the measurements based on the kTkT jet algorithm is αs(MZ)=0.1206−0.0022+0.0023(exp.)−0.0035+0.0042(th.); the results from the anti-kTkT and SIScone algorithms are compatible with this value and have a similar precision.