System size and beam energy effects on probing the high-density behavior of nuclear symmetry energy with pion ratio Original Research Article

Based on the isospin-and momentum-dependent hadronic transport model IBUU04, we have investigated the π−/π+ ratio in the following three reactions: 48Ca+48Ca, 124Sn + 124Sn and 197Au + 197Au with nearly the same isospin asymmetry but different masses, at the bombarding energies from 0.25 to 0.6 AGeV. It is shown that the sensitivity of probing the Esym(ρ) with π−/π+ increases with increasing the system size or decreasing the beam energy, showing a correlation to the degree of isospin fractionation. Therefore, with a given isospin asymmetry, heavier system at energies near the pion threshold is preferential to study the behavior of nuclear symmetry energy at supra-saturation densities.