Single and double π-/π+ ratios in heavy-ion reactions as probes of the high-density behavior of the nuclear symmetry energy

Based on the isospin- and momentum-dependent hadronic transport model IBUU04, effects of the nuclear symmetry energy on the single and double pi(-)/pi(+) ratios in central reactions of Sn-132+Sn-124 and Sn-112+Sn-112 at a beam energy of 400 MeV/nucleon are studied. It is found that around the Coulomb peak of the single pi(-)/pi(+) ratio the double pi(-)/pi(+) ratio taken from the two isotopic reactions retains about the same sensitivity to the density dependence of nuclear symmetry energy. Because the double pi(-)/pi(+) ratio can significantly reduce the systematic errors, it is thus a more effective probe for the high-density behavior of the nuclear symmetry energy.