ENTROPY PRODUCTION IN THE AU-A AND 800-A MEV(AU REACTION BETWEEN 150)

The entropy per nucleon (S/A) has been extracted for the Au [(150-800) A MeV] + Au reaction by using the phase I setup of the 4pi facility at GSI, Darmstadt. The entropy has been obtained from the comparison of various observables characterizing the dM/dZ fragment multiplicity dis tributions, extending up to Z is similar to 15, with those calculated with the quantum statistical model. It is the first time that S/A valu es are determined by considering the full ensemble of charged products detected in the reaction. Consistent values of S/A are found from dif ferent methods. These entropy values are shown to be fairly independen t of the volume of the ''participant'' region considered. They are som ewhat lower than those extracted in earlier works but are in good agre ement with hydrodynamic calculations and suggest a low viscosity for t he hot and dense nuclear matter.