Sensitivity of neutron to proton ratio toward the high density behavior of the symmetry energy in heavy-ion collisions

The symmetry energy at sub- and supra-saturation densities has great importance for understanding the exact nature of asymmetric nuclear matteras well as neutron stars, but it is poorly known, especially at supra-saturation densities. We will demonstrate here whether or not the neutron-to-proton ratios from different kinds of fragments can determine the supra-saturation behavior of the symmetry energy. For this purpose, a series of Sn isotopes were simulated at different incident energies using the isospinquantum molecular dynamics (IQMD) model with either a soft or a stiff symmetry energy. It is found that the single neutron-to-proton ratio from free nucleons as well as Light Charged Particles (LCPs) is sensitive to the symmetry energy, incident energy, and isospinasymmetry of the system. However, with the double neutron-to-proton ratio, this is true only for the free nucleons. It is possible to study the high-density behavior of symmetry energy by using the neutron-to-proton ratio from free nucleons.