Measurement of subjet multiplicities in neutral current deep inelastic scattering at HERA and determination of αs
Abstract
The subjet multiplicity has been measured in neutral current e+p interactions at Q**2 > 125 GeV**2 with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb-1. Jets were identified in the laboratory frame using the longitudinally invariant KT cluster algorithm. The number of jet-like substructures within jets, known as the subjet multiplicity, is defined as the number of clusters resolved in a jet by reapplying the jet algorithm at a smaller resolution scale ycut. Measurements of the mean subjet multiplicity, < nsbj >, for jets with transverse energies ET,jet >15 GeV are presented. Next-to-leading-order perturbative QCD calculations describe the measurements well. The value of alphas(MZ), determined from < nsbj > at ycut=10**-2 for jets with 25 < ET,jet < 71 GeV, is alphas (MZ) = 0.1187 +/- 0.0017 (stat.) +0.0024 / -0.0009 (syst.) +0.0093 / -0.0076 (th.).
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