Beam Energy Dependence of the π^-/π⁺ Ratio

Using the isospin- and momentum-dependent hadronic transport model IBUU04, the effects of symmetry energy on the π^-/π⁺ ratio are studied. Our investigations are based on the calculations of the ¹³²Sn+¹²⁴Sn semi-central collisions at beam energies of 400/A MeV, 600/A MeV and 800/A MeV. It is found that both the transverse momentum and kinetic energy distributions of the π^-/π⁺ ratio are rather sensitive to the symmetry energy, especially around the Coulomb peaks. The position of the Coulomb peak is shown to be nearly independent of beam energy. The sensitivity of the π^-/π⁺ ratio to the symmetry energy decreases as the beam energy increases from 600/A MeV to 800/A MeV.