Measurement of Event Shape Variables in Deep-Inelastic Scattering at HERA

TL;DR

This paper analyzes event shape variables in deep-inelastic scattering at HERA, demonstrating the running of the strong coupling and extracting QCD parameters through comparison with theoretical models.

Contribution

It provides the first comprehensive measurement of multiple event shape variables in DIS and tests perturbative QCD predictions including non-perturbative corrections.

Findings

Data confirms the running of alpha_s(Q)

Universal power correction parameter alpha_0 fits all variables

QCD fit yields alpha_s(mZ) = 0.1198 ± 0.0013

Abstract

Deep-inelastic ep scattering data taken with the H1 detector at HERA and corresponding to an integrated luminosity of 106 pb^{-1} are used to study the differential distributions of event shape variables. These include thrust, jet broadening, jet mass and the C-parameter. The four-momentum transfer Q is taken to be the relevant energy scale and ranges between 14 GeV and 200 GeV. The event shape distributions are compared with perturbative QCD predictions, which include resummed contributions and analytical power law corrections, the latter accounting for non-perturbative hadronisation effects. The data clearly exhibit the running of the strong coupling alpha_s(Q) and are consistent with a universal power correction parameter alpha_0 for all event shape variables. A combined QCD fit using all event shape variables yields alpha_s(mZ) = 0.1198 \pm 0.0013 ^{+0.0056}_{-0.0043} and alpha_0 = 0.476 \pm 0.008 ^{+0.018} _{-0.059}.