We show that the transverse-mass and rapidity spectra of protons and pions produced in Au-Au collisions at $\sqrt{s_{\mathrm{NN}}}=2.4$ GeV can be well reproduced in a thermodynamic model assuming single freeze-out of particles from a spherically symmetric hypersurface. This scenario corresponds to a physical picture used by Siemens and Rasmussen in the original formulation of the blast-wave model. Our framework modifies and extends this approach by incorporation of a Hubble-like expansion of QCD matter and inclusion of resonance decays. In particular, the $\mathrm{\Delta }\left(1232\right)$ resonance is taken into account, with a width obtained from the virial expansion. Altogether, our results bring evidence for substantial thermalization of the matter produced in heavy-ion collisions in the few-GeV energy regime and its nearly spherical expansion.

• Received 29 April 2020
• Revised 2 July 2020
• Accepted 22 September 2020

DOI:https://doi.org/10.1103/PhysRevC.102.054903