Nuclear system size scan for freeze-out properties in relativistic heavy-ion collisions by using a multiphase transport model

Abstract

A system size scan program was recently proposed for the STAR experiments at the Relativistic Heavy Ion Collider(RHIC). In this study, we employ a multiphase transport (AMPT) model for considering the bulk properties at the freeze-out stage for ${}^{10}\mathrm{B}{+}^{10}\mathrm{B}$, ${}^{12}\mathrm{C}{+}^{12}\mathrm{C}$, ${}^{16}\mathrm{O}{+}^{16}\mathrm{O}$, ${}^{20}\mathrm{Ne}{+}^{20}\mathrm{Ne}$, ${}^{40}\mathrm{Ca}{+}^{40}\mathrm{Ca}$, ${}^{96}\mathrm{Zr}{+}^{96}\mathrm{Zr}$, and ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ collisions at RHIC energies $\sqrt{s_{NN}}$ of 200, 20, and 7.7 GeV. The results for ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ collisions are comparable with those of previous experimental STAR data. The transverse momentum $p_T$ spectra of charged particles ($\ddot{I}{€}^{\pm }$, $K^{\pm }$, $p$, and $\bar{p}$) at the kinetic freeze-out stage, based on a blast-wave model, are also discussed. In addition, we use a statistical thermal model to extract the parameters at the chemical freeze-out stage, which agree with those from other thermal model calculations. It was found that there is a competitive relationship between the kinetic freeze-out parameter $T_{kin}$ and the radial expansion velocity ${\hat{I}}_T^2$, which also agrees with the STAR or ALICE results. We found that the chemical freeze-out strangeness potential $\hat{I}{¼}_s$ remains constant in all collision systems and that the fireball radius $R$ is dominated by $⟨{\mathrm{N}}_{\mathrm{Part}}⟩$, which can be well fitted by a function of $a{⟨{\mathrm{N}}_{\mathrm{Part}}⟩}^b$ with $b\approx 1/3$. In addition, we calculated the nuclear modification factors for different collision systems with respect to the ${}^{10}\mathrm{B}+{}^{10}\mathrm{B}$ system, and found that they present a gradual suppression within a higher $p_T$ range from small to large systems.

10 pages, 8 figures, 3 tables