Near-threshold pion production with radioactive beams at the Rare Isotope Accelerator

Using an isospin- and momentum-dependent transport model we study near-threshold pion production in heavy-ion collisions induced by radioactive beams at the planned Rare Isotope Accelerator (RIA). We revisit the question of probing the high density behavior of nuclear symmetry energy $E_{sym}(\rho)$ using the $\pi^-/\pi^+$ ratio. It is found that both the total and differential $\pi^-/\pi^+$ ratios remain sensitive to the $E_{sym}(\rho)$ when the momentum-dependence of both the isoscalar and isovector potentials are consistently taken into account. Moreover, the multiplicity and spectrum of $\pi^-$ mesons are found more sensitive to the $E_{sym}(\rho)$ than those of $\pi^+$ mesons. Finally, effects of the Coulomb potential on the pion spectra and $\pi^-/\pi^+$ ratio are also discussed.