Multiplicity Distributions of Intermediate Mass Fragments in the Thermodynamic Model

Multiplicity distributions of intermediate mass fragments (IMF) seen in intermediate energy heavy ion collisions have been of great interest in the last ten years. The distributions of single intermediate sized element are close to Poissonian and have been subjected to widely different physical interpretations. We calculate the multiplicity distributions in a thermodynamic model whose physical basis is equal population in phase space which implies equilibrium statistics. We found distributions of single element are to a good approximation Poissonian, and such result is attributed to the small emission probability of a given IMF among all the possible channels. We also found significant deviation from Poisson distribution for a range of IMFs, and suggest strong correlations as an explanation. Systematics of the multiplicity distributions are explored in both one component and two component models. In one component model, sudden changes for the multiplicity distributions are found at the phase transition region. In two component model, the multiplicity distributions have more subtleties. Results from the current model are compared with available data, and good agreements are found. New signals for the multi-particle correlations are also suggested.