The negative binomial distribution in quark jets with fixed flavour

We show that both the multiplicity distribution and the ratio of factorial cumulants over factorial moments for 2-jet events in e+e− annihilation at the Z0 peak can be well reproduced by the weighted superposition of two negative binomial distributions, associated to the contribution of bb and light flavoured events respectively. The negative binomial distribution is then suggested to describe the multiplicity distribution of 2-jet events with fixed flavour.