Energy dependence of the entropy production in relativistic heavy-ion collisions

We compile experimental data on the production yields of protons, deuterons, and pions from 1 to 200 GeV of √S _NN, and interpret them in the context of the nucleon density of a hot, dense fireball and the entropy production. The d/p yield ratio decreases with beam energy, implying that the nucleon density also decreases with beam energy. However, the entropy per nucleon increases with beam energy. In particular, the rate of the entropy increase changes dramatically at √S _NN ≃ 2 GeV, where nuclear stopping and sideward flow show their maxima. We conclude that disassembled nucleons are more effective for the entropy production than particle production. A big change in the energy dependence of the entropy production has not been observed between the Alternating Gradient Synchrotron (AGS) and the Relativistic Heavy Ion Collider (RHIC) energies.