Hierarchy of kinetic freeze-out parameters in low-energy heavy-ion collisions

Abstract

We study the mass-dependent hierarchy of kinetic freeze-out parameters of hadrons in low-energy heavy-ion collisions. For this purpose, the transverse momentum and rapidity spectra of the identified hadrons produced in central Pb+Pb collisions, available at super proton synchrotron energies ranging from ELab=20A-158A GeV, are analyzed within a generalized non-boost-invariant blast-wave model. We consider separate simultaneous fits for light hadrons (π-, K±) and heavy strange hadrons (Λ, Λ¯, φ, Ξ±, ω±), for which the transverse momentum spectra as well as rapidity spectra are available. We also perform a separate fit to transverse momentum spectra of charmonia (J/ψ, ψ′) at 158A GeV collisions. We find a clear mass-dependent hierarchy in the fitted kinetic freeze-out parameters. Further, we study the rapidity spectra using analytical Landau flow solution for nonconformal systems. We find that the fitted value of sound velocity in the medium also shows a similar hierarchy. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.