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 SPS energies ranging from $\rm E_{Lab}=20A-158A $ GeV, are analyzed within a generalized non boost-invariant blast wave model. We consider separate simultaneous fits for light hadrons ($\pi^{-}$, $K^{\pm}$) and heavy strange hadrons ($\Lambda$, $\bar{\Lambda}$, $\phi$, $\Xi^{\pm}$, $\Omega^{\pm}$), 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 ($J/\Psi$, $\Psi'$) 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 non-conformal systems. We find that the fitted value of sound velocity in the medium also shows a similar hierarchy.