Σ−/Σ+ratio as a candidate for probing the density dependence of the symmetry potential at high nuclear densities

Abstract

Based on the UrQMD (ultrarelativistic quantum molecular dynamics) model, we have investigated the influence of the symmetry potential on the negatively and positively charged $\ensuremath{\pi}$ and $\ensuremath{\Sigma}$ hyperon production ratios in heavy ion collisions at the SIS (SchwerIonen Synchrotron) energies. We find that, in addition to ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratio, the ${\ensuremath{\Sigma}}^{\ensuremath{-}}/{\ensuremath{\Sigma}}^{+}$ ratio can be taken as a sensitive probe for investigating the density dependence of the symmetry potential of nuclear matter at high densities (1--4 times normal baryon density). This sensitivity of the symmetry potential to both the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ and ${\ensuremath{\Sigma}}^{\ensuremath{-}}/{\ensuremath{\Sigma}}^{+}$ ratios is found to depend strongly on the incident beam energy. Furthermore, the ${\ensuremath{\Sigma}}^{\ensuremath{-}}/{\ensuremath{\Sigma}}^{+}$ ratio is shown to carry the information about the isospin-dependent part of the $\ensuremath{\Sigma}$ hyperon single-particle potential.