Probing high-density symmetry energy using heavy-ion collisions at intermediate energies

TL;DR

This paper advances the understanding of high-density nuclear symmetry energy by developing sophisticated transport models and proposing new observables in heavy-ion collisions to better probe its behavior at supra-saturation densities.

Contribution

It introduces an improved isospin-dependent transport model incorporating new physics and identifies novel sensitive probes for high-density symmetry energy, including the effects of nucleon correlations.

Findings

New sensitive probes such as neutron-to-proton ratio, photon, and meson production.

Model dependence of symmetry energy probes has been thoroughly studied.

Effects of nucleon-nucleon correlations on observables have been analyzed.

Abstract

The nuclear symmetry energy, which describes the energy difference of per proton and neutron in nuclear matter, has been extensively studied within the last two decades. Around saturation density, both the value and the slope of the nuclear symmetry energy have been roughly constrained, its high-density behavior is now still in argument. Probing high-density symmetry energy at terrestrial laboratories is being carried out at facilities that offer radioactive beams worldwide. While relevant experiments are being conducted, we theoretically developed more advanced isospin-dependent transport model including new physics such as nucleon-nucleon short-range correlations and in-medium isospin-dependence of baryon-baryon scattering cross section. New sensitive probes of high-density symmetry energy are provided, such as squeezed-out neutron to proton ratio, photon and light cluster as well as the production of mesons with strangeness or hidden strangeness. The blind spots of probing the high-density symmetry energy by sensitive observable are demonstrated. Model dependence of frequently used sensitive probes of the symmetry energy has been studied thoroughly based on different transport models. A qualitative observable of neutron to proton ratio at high emitting energy is proposed to probe the high-density symmetry energy qualitatively. The probed density regions of the symmetry energy are carefully studied. Effects of nucleon-nucleon short-range correlations on the some sensitive observables of the symmetry energy in heavy-ion collisions are explored carefully. Probing the curvature of the symmetry energy by involving the slope information of the symmetry energy at saturation point in the transport model is proposed.