Moments of the charged-particle multiplicity distribution in Z decays at LEP

Abstract

The charged-particle multiplicity distribution and its moments have been measured, for all hadronic as well as for light-quark and b-quark events in e+e- collisions at the Z mass. The Hq moments derived from the charged-particle multiplicity distribution are known to exhibit quasi-oscillations when plotted versus the order of the moment. This behavior is predicted by the NNLLA of perturbative QCD for the parton level and, under the assumption of LPHD, also for the hadron level. Using the jet multiplicity distributions in order to vary the dependence on the LPHD hypothesis, we find, however, that at our energy the oscillations only appear for non-perturbative scales. In the absence of confirmation of pQCD, we investigate a more phenomenological answer in the possibility that the features seen in the Hq behavior could be due to the fact that the charged-particle multiplicity derives from a superposition of final states related to the topology of the events. Therefore, the analysis is repeated using charged-particle multiplicity distributions originating from 2-jet and 3-jet events for the full, light- and b-quark samples.