Study of quark fragmentation in e+e- annihilation at 29 GeV: Charged-particle multiplicity and single-particle rapidity distributions

This paper presents the charged-particle multiplicity distributions for e+e- annihilation at s =29 GeV measured in the High Resolution Spectrometer. The data, which correspond to an integrated luminosity of 185 pb-1, were obtained at the SLAC e+e- storage ring PEP. The techniques used to correct the observed prong numbers are discussed. The multiplicity distribution of the charged particles has a mean value n=12.87±0.03±0.30, a dispersion D2=3.67±0.02±0.18, and an f2 moment of 0.60±0.02±0. 18. Results are also presented for a two-jet sample selected with low sphericity and aplanarity. The charged-particle distributions are almost Poissonian and narrower than have been reported by other e+e- experiments in this energy range. The mean multiplicity increases with the event sphericity, and for the sample of threefold-symmetric three-jet events, a value of n=16.3±0.3±0.7 is found. No correlation is observed between the multiplicities in the two hemispheres when the events are divided into two jets by a plane perpendicular to the thrust axis. This result is in contrast with the situation in soft hadronic collisions, where a strong forward-backward correlation is measured. For the single jets, a mean multiplicity of 6.43±0.02±0.15 and a dispersion value of D2=2.55±0.02±0.13 are found. These values give further support to the idea of independent jet fragmentation. The multiplicity distributions are well fit by the negative-binomial distribution. The semi-inclusive rapidity distributions are presented. Comparisons are made to the measurements of charged-particle multiplicities in hadron-hadron and lepton-nucleon collisions.