Directed and elliptic flow observations in Sn+Sn collisions with radioactive beams at 270 MeV/u

Abstract

Radioactive tin beams were used to explore the flow observables under varying isospin asymmetries while maintaining a constant total charge. The rapidity dependence of directed flow ($v_1$) and elliptic flow ($v_2$) was studied for protons, deuterons, tritons, ${}^3\mathrm{H}e$, and ${}^4\mathrm{H}e$, produced in neutron-rich ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ and neutron-deficient ${}^{108}\mathrm{S}n+{}^{112}\mathrm{S}n$ collisions at 270 $\mathrm{MeV}/\text{nucleon}$. In general, heavier particles exhibited larger $v_1$ and $v_2$ values. The experimental data was used to test transport models which simulate heavy ion collisions. Specifically, comparisons were made with Antisymmetrized Molecular Dynamics (AMD) model calculations, which explicitly account for cluster correlations. Two types of momentum-dependent mean field potentials were tested. The results reveal that both $v_1$ and $v_2$ values are enhanced when the mean field incorporates stronger momentum dependence. In addition, $v_2$ exhibits larger sensitivity to symmetry energy than $v_1$ but the overall sensitivity to symmetry energy is low. In an attempt to describe the data, different parameter sets have been tried. Most describe either the hydrogen flow or helium flow reasonably well but none describes the flow of all particles simultaneously.