Eur. Phys. J. A (2020) 56: 267
https://doi.org/10.1140/epja/s10050-020-00273-y

Regular Article - Theoretical Physics

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

¹ Institut für Theoretische Physik, Goethe Universität Frankfurt, Max-von-Laue-Str. 1, 60438, Frankfurt am Main, Germany
² Helmholtz Research Academy Hesse for FAIR, Campus Frankfurt, Max-von-Laue-Str. 12, 60438, Frankfurt, Germany
³ Department of Physics, University of Jyväskylä, PO Box 35, 40014, Jyväskylä, Finland
⁴ Helsinki Institute of Physics, University of Helsinki, PO Box 64, 00014, Helsinki, Finland
⁵ GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstr. 1, 64291, Darmstadt, Germany
⁶ John von Neumann-Institut für Computing, Forschungszentrum Jülich, 52425, Jülich, Germany

^* e-mail: treichert@itp.uni-frankfurt.de

Received: 15 July 2020
Accepted: 5 October 2020
Published online: 20 October 2020

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 $$\langle E\rangle /\langle N\rangle \approx 1$$ 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.