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

Abstract Differential inclusive-jet cross sections have been measured for different jet radii in neutral current deep inelastic ep scattering for boson virtualities Q 2 > 125 GeV 2 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 Q 2 and the jet transverse energy, E T , B jet . The dependence on R of the inclusive-jet cross section has been measured for Q 2 > 125 and 500 GeV 2 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 d σ / d Q 2 with R = 1 for Q 2 > 500 GeV 2 : 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.