Near-threshold pion production with radioactive beams

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 Esym(ρ) using the π^-/π⁺ ratio. It is found that both the total and differential π^-/π⁺ ratios remain sensitive to the Esym(ρ) when the momentum-dependence of both the isoscalar and isovector potentials are consistently taken into account. Moreover, the multiplicity and spectrum of π^- mesons are found more sensitive to the Esym(ρ) than those of π⁺ mesons. Finally, effects of the Coulomb potential on the pion spectra and π^-/π⁺ ratio are also discussed.