Probing heavy-ion collisions with the yield ratios of neutron-proton at intermediate energy

Abstract

Within an isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, we investigate effects of nucleon-nucleon short-range correlations (SRCs) and the nuclear symmetry energy on the yield ratios of neutron-proton (n/p) in four reaction systems K94r+94Kr, Z94r+94Zr, M94o+94Mo and R94u+94Ru. It is found that effects of the symmetry energy and the high momentum tails (HMTs), caused by the SRCs of nucleon-nucleon in the target and projectile, on the kinetic energy distribution of n/p yield ratio are almost same in four reaction systems. While the effect of the HMTs on the double ratio of n/p from neutron-rich and neutron-deficient reaction systems K94r+94Kr and R94u+94Ru is enlarged, and it is about two times than that of the symmetry energy in the high kinetic energies. Meanwhile, we find that the dependence of isospin-fractionation (i.e., the double ratio of n/p of gas-liquid phase) on the isospin asymmetry of reaction system is completely not sensitive to the HMTs but keeping high sensitivity to the symmetry energy. It indicates that the distribution of isospin-fractionation on the isospin asymmetry of reaction system can be taken as an experimental observable to extract information on nuclear symmetry energy.