Transverse energy per charged particle and freeze-out criteria in heavy-ion collisions

In relativistic nucleus–nucleus collisions the transverse energy per charged particle, ET/NchET/Nch, increases rapidly with beam energy and remains approximately constant at about 800 MeV for beam energies from SPS to RHIC. It is shown that the hadron resonance gas model describes the energy dependence, as well as the lack of centrality dependence, qualitatively. The values of ET/NchET/Nch are related to the chemical freeze-out criterium E/N≈1 GeVE/N≈1 GeV valid for primordial hadrons.