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 E${}_{\mathrm{lab}}=1.23$ AGeV to $\sqrt{s_{\mathrm{NN}}}=62.4$ 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 $⟨E⟩/⟨N⟩\approx 1$ GeV, while other criteria, like $s/T^3=7$ and $n_{\mathrm{B}}+n_{\bar{\mathrm{B}}}\approx 0.12$ fm${}^{-3}$ are limited to higher collision energies.

arXiv comment9 pages, 10 figures

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