Are heavy-ion entropy production and nuclear level density discrepancies related?

Abstract

The thermodynamic properties of a system of Dirac particles interacting through classical fields are studied within the interaction models proposed recently. The theoretical formalism is based on the variational ansatz of the Gibbs free energy. The binding energy per nucleon, pressure and specific entropy are calculated from the low-temperature expansion in the range of densities and temperatures of interest to heavy-ion reactions. The calculated value of specific entropy produced in heavy-ion collisions is found to be much less than that obtained from the measured value of the deuteron to proton ratio. The model of Boguta and Bodmer (1977) predicts larger values of the specific entropy as compared with those of the Walecka model. It is pointed out that the difficulty of understanding the nuclear level density data may be related to that of the entropy production in heavy-ion reactions. A relativistic generalisation of Bethe's level density parameter and the average thermal energy, useful in hydrodynamic calculations, are derived.