Effects of the momentum dependence of nuclear symmetry potential on pion observables in Sn + Sn collisions at 270 MeV/nucleon

Abstract

Within a transport model, we study effects of the momentum dependence of nuclear symmetry potential on pion observables in central Sn + Sn collisions at 270 MeV/nucleon. To this end, a quantity $U_{sym}^{\infty }({\rho }_0)$, i.e., the value of nuclear symmetry potential at the saturation density ${\rho }_0$ and infinitely large nucleon momentum, is used to characterise the momentum dependence of nuclear symmetry potential. It is shown that with a certain $L$ (i.e., slope of nuclear symmetry energy at ${\rho }_0$) the characteristic parameter $U_{sym}^{\infty }({\rho }_0)$ of symmetry potential affects significantly the production of ${\pi }^{-}$ and ${\pi }^{+}$ as well as their pion ratios. Moreover, through comparing the charged pion yields, pion ratios as well the spectral pion ratios of theoretical simulations for the reactions ${}^{108}$Sn + ${}^{112}$Sn and ${}^{132}$Sn + ${}^{124}$Sn with the corresponding data in S$\pi$RIT experiments, we find that our results favor a constraint on $U_{sym}^{\infty }({\rho }_0)$, i.e., $-160_{-9}^{+18}$~MeV, and the $L$ is also suggested within a range, i.e., $62.7<L<93.1$~MeV. In addition, it is shown that the pion observable of ${}^{197}$Au + ${}^{197}$Au collisions at 400~MeV/nucleon also supports the extracted value for $U_{sym}^{\infty }({\rho }_0)$.

Comments: 11 pages, 14 figures, add several references and several figures to interpret the results; original conclusion is not changed qualitatively, more stringent constraints on $U_{sym}^{\infty }({\rho }_0)$ are concluded quantitatively. Accepted for publication in Nuclear Science and Techniques