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 investigated the effects of the momentum dependence of the nuclear symmetry potential on the pion observables in central Sn + Sn collisions at 270 MeV/nucleon. To this end, the quantity \(U_\text {sym}^{\infty }(\rho _{0})\) (i.e., the value of the nuclear symmetry potential at the saturation density \(\rho _{0}\) and infinitely large nucleon momentum) was used to characterize the momentum dependence of the nuclear symmetry potential. With a certain L (i.e., the slope of the nuclear symmetry energy at \(\rho _{0}\)), the characteristic parameter \(U_\text {sym}^{\infty }(\rho _{0})\) of the symmetry potential significantly affects the production of \(\pi ^{-}\) and \(\pi ^{+}\) and their pion ratios. Moreover, by comparing the charged pion yields, pion ratios, and spectral pion ratios of the theoretical simulations for the reactions \(^{108}\)Sn + \(^{112}\)Sn and \(^{132}\)Sn + \(^{124}\)Sn with the corresponding data in the S\(\pi \)RIT experiments, we found that our results favor a constraint on \(U_\text {sym}^{\infty }(\rho _{0})\) (i.e., \(-160^{+18}_{-9}\) MeV), and L is also suggested within a range of 62.7 MeV\(<L<93.1\) MeV. In addition, the pion observable for \(^{197}\)Au + \(^{197}\)Au collisions at 400 MeV/nucleon also supports the extracted value for \(U_\text {sym}^{\infty }(\rho _{0})\).