Measurement of subjet multiplicities in neutral current deep inelastic scattering at HERA and determination of alpha(s)

Abstract The subjet multiplicity has been measured in neutral currente + p interactions at Q 2 >125 GeV 2 with the ZEUS detector at HERAusing an integrated luminosity of 38.6 pb −1 . Jets were identified in the laboratory frame using the longitudinally invariant k T 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 y cut . Measurements of the mean subjet multiplicity, 〈 n sbj 〉, for jets with transverse energies E T,jet >15 GeV are presented. Next-to-leading-order perturbative QCDcalculations describe the measurements well. The value of α s ( M Z ), determined from 〈 n sbj 〉 at y cut =10 −2 for jets with 25 E T,jet α s ( M Z )=0.1187±0.0017(stat.) +0.0024 −0.0009 (syst.) +0.0093 −0.0076 (th.).