Probing chemical freeze-out criteria in relativistic nuclear collisions with coarse grained transport simulations

Abstract

We introduce a novel approach based on elastic and inelastic scattering rates to extract the hyper-surface of the chemical freeze-out from a hadronic transport model in the energy range from Elab = 1.23 AGeV to √sNN = 62.4 GeV. For this study, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model combined with a coarse-graining method is employed. The chemical freeze-out distribution is reconstructed from the pions through several decay and re-formation chains involving resonances and taking into account inelastic, pseudo-elastic and string excitation reactions. The extracted average temperature and baryon chemical potential are then compared to statistical model analysis. Finally we investigate various freeze-out criteria suggested in the literature. We confirm within this microscopic dynamical simulation, that the chemical freeze-out at all energies coincides with ⟨E⟩/⟨N⟩ ≈1 GeV, while other criteria, like s/T3 = 7 and nB+nB¯ ≈ 0.12 fm−3 are limited to higher collision energies.