Shedding light on the pion production in heavy-ion collisions and application into the neutron star matter properties

Abstract

Within the framework of the quantum molecular dynamics transport model, the pion production and constraint of the high-density symmetry energy in heavy-ion collisions near threshold energy have been thoroughly investigated. The energy conservation in the decay of resonances and reabsorption of pions as well as in the inelastic nucleon-nucleon and nucleon-resonance collisions are taken into account. The isospin diffusion in the low-density region (0.2${\rho }_0$ - 0.8${\rho }_0$) and high-density region (1.2${\rho }_0$ - 1.8${\rho }_0$) is investigated by analyzing the spectra of neutron/proton and ${\pi }^{-}/{\pi }^{+}$ ratios in the isotopic reactions of ${}^{132}$Sn + ${}^{124}$Sn and ${}^{108}$Sn + ${}^{112}$Sn at the incident energy of 270 MeV/nucleon, in which the symmetry energy manifests the opposite effect in the different density domain. The controversial conclusion of the ${\pi }^{-}/{\pi }^{+}$ ratio for constraining the high-density symmetry energy by different transport models with the FOPI data has been clarified. A soft symmetry energy with the slope parameter of $L({\rho }_0)=42\pm 25$ MeV by using the standard error analysis within the range of $1\sigma$ is obtained by analyzing the experimental data from the S$\pi$RIT collaboration. The neutron stars with the maximal mass of 2 $M_{\odot }$ and radius of 11-13 km are obtained with the constrained symmetry energy.

Comments: 10 pages, 8 figures