Multiplicity and bombarding energy dependence of the entropy in relativistic heavy-ion reactions

The yield ratios of light clusters (d,t${,}^3$He,α) to protons were measured for the reactions Nb + Nb and Au+Au for incident beam energies of 150, 250, 400, and 650 MeV/nucleon. The ratios are analyzed in the framework of the quantum statistical model and the specific entropy is extracted as a function of the participant proton multiplicity. The results are compared with predictions of the fireball model and relativistic mean field calculations.