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Abstract
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.