Rapidity and energy dependence of thermal parameters

For beam energies from SPS to RHIC, the transverse energy per charged particle, E_T/N_ch, saturates at a value of approximately 0.8 GeV. A direct connection between this value and the freeze-out criterium E/N ≈ 1 GeV for the primordial energy and particle number in the hadronic resonance gas model is established. The rapidity dependence of the chemical freeze-out thermal parameters T and μ_B is determined at the highest RHIC and SPS energies. These show a systematic increase in μ_B away from mid-rapidity and a corresponding decrease in the temperature T.