Charged-particle multiplicity has been studied in e + e \Gamma annihilation reaction at p s = 57:8GeV using the TOPAZ detector at TRISTAN. The average multiplicity is found as hn ch i = 17:64 \Sigma 0:05(stat:) \Sigma 0:43(syst:). It is consistent with the theoretical calculation based on the Modified Leading-Log Approximation together with the available other experimental measurements at 12GeV ! p s ! 91:2GeV. It is found that the multiplicity depends on the thrust (T ) of an event. This is a direct evidence for the difference in the multiplicity of a quark-jet from a gluon-jet. By extrapolating this dependence to T = 2=3, the multiplicity for three-fold symmetric events is estimated to be hn ch i T=2=3 = 23:50 +1:25 \Gamma1:45 . From this, the multiplicity ratio between a gluon- and a quark-jet has been estimated to be r g=q = 1:46 +0:09 \Gamma0:13 without any possible bias from jet clustering. Contents 1 Introduction 1 2 Theoretical Background about Particle Multiplici..
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