Multiplicity distributions and rapidity gaps

We examine the phenomenology of particle multiplicity distributions, with special emphasis on the low multiplicities that are a background to the study of rapidity gaps. In particular, we analyze the multiplicity distribution in a rapidity interval between two jets, using the herwig QCD simulation with some necessary modifications. The distribution is not of the ``negative binomial'' form, and displays an anomalous enhancement at zero multiplicity. Some useful mathematical tools for working with multiplicity distributions are presented. It is demonstrated that ignoring particles with p_⊥0.2 GeV/c has theoretical advantages, in addition to being convenient experimentally.