Probing the density dependence of the symmetry potential in intermediate energy heavy ion collisions

Based on the ultrarelativistic quantum molecular dynamics (UrQMD) model, the effects of the density-dependent symmetry potential for baryons and of the Coulomb potential for produced mesons are investigated for neutron-rich heavy ion collisions at intermediate energies. The calculated results of the $Delta^-/Delta^{++}$ and $pi ^{-}/pi ^{+}$ production ratios show a clear beam-energy dependence on the density-dependent symmetry potential, which is stronger for the $pi ^{-}/pi ^{+}$ ratio close to the pion production threshold. The Coulomb potential of the mesons changes the transverse momentum distribution of the $pi ^{-}/pi ^{+}$ ratio significantly, though it alters only slightly the $pi^-$ and $pi^+$ total yields. The $pi^-$ yields, especially at midrapidity or at low transverse momenta and the $pi^-/pi^+$ ratios at low transverse momenta, are shown to be sensitive probes of the density-dependent symmetry potential in dense nuclear matter. The effect of the density-dependent symmetry potential on the production of both, K$^0$ and K$^+$ mesons, is also investigated.