Jet-radius dependence of inclusive-jet cross sections in deep inelastic scattering at HERA

Differential inclusive-jet cross sections have been measured for different jet radii in neutral current deep inelastic ep scattering for boson virtualities Q² > 125 GeV² with the ZEUS detector at HERA using an integrated luminosity of 81.7 pb^-1. Jets were identified in the Breit frame using the k_T cluster algorithm in the longitudinally inclusive mode for different values of the jet radius R. Differential cross sections are presented as functions of Q² and the jet transverse energy, E_T,B^jet. The dependence on R of the inclusive-jet cross section has been measured for Q² > 125 and 500 GeV² and found to be linear with R in the range studied. Next-to-leading-order QCD calculations give a good description of the measurements for 0.5 ⩽ R ⩽ 1. A value of α_s (M_Z) has been extracted from the measurements of the inclusive-jet cross section dσ / dQ² with R = 1 for Q² > 500 GeV²: α_s (M_Z) = 0.1207 ± 0.0014 (stat .)_-0.0033^+0.0035 (exp .) -0.0023 +0.0022 (th .). The variation of α_s with E_T,B^jet is in a good agreement with the running of α_s as predicted by QCD.