Professor Amanda Cooper-Sarkar

Abstract:

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 kT 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, ET, Bjet. 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 αs (MZ) has been extracted from the measurements of the inclusive-jet cross section d σ / d Q2 with R = 1 for Q2 > 500   GeV2: αs (MZ) = 0.1207 ± 0.0014 (stat .)-0.0033+0.0035 (exp .)-0.0023+0.0022 (th .). The variation of αs with ET, Bjet is in a good agreement with the running of αs as predicted by QCD. © 2007 Elsevier B.V. All rights reserved.

Abstract:

Mean values and differential distributions of event-shape variables have been studied in neutral current deep inelastic scattering using an integrated luminosity of 82.2 pb-1 collected with the ZEUS detector at HERA. The kinematic range is 80 < Q2 < 20 480 GeV2 and 0.0024 < x < 0.6, where Q2 is the virtuality of the exchanged boson and x is the Bjorken variable. The data are compared with a model based on a combination of next-to-leading-order QCD calculations with next-to-leading-logarithm corrections and the Dokshitzer-Webber non-perturbative power corrections. The power-correction method provides a reasonable description of the data for all event-shape variables studied. Nevertheless, the lack of consistency of the determination of αs and of the non-perturbative parameter of the model, over(α0, -), suggests the importance of higher-order processes that are not yet included in the model. © 2006 Elsevier B.V. All rights reserved.