Entropy production in the Au+Au reaction between 150Aand 800AMeV

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Abstract
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 4π facility at GSI, Darmstadt. The entropy has been obtained from the comparison of various observables characterizing the dM/dZ fragment multiplicity distributions, extending up to Z∼15, with those calculated with the quantum statistical model. It is the first time that S/A values are determined by considering the full ensemble of charged products detected in the reaction. Consistent values of S/A are found from different methods. These entropy values are shown to be fairly independent of the volume of the ‘‘participant’’ region considered. They are somewhat lower than those extracted in earlier works but are in good agreement with hydrodynamic calculations and suggest a low viscosity for the hot and dense nuclear matter.