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

TL;DR

This study investigates how neutron to proton ratios from heavy-ion collision fragments can reveal the high-density behavior of nuclear symmetry energy, using simulations of Sn isotopes with different symmetry energy models.

Contribution

It demonstrates that neutron to proton ratios from free nucleons effectively probe the supra-saturation symmetry energy behavior in heavy-ion collisions.

Findings

Single neutron to proton ratio is sensitive to symmetry energy, incident energy, and isospin asymmetry.

Double neutron to proton ratio is sensitive only for free nucleons.

Neutron to proton ratio from free nucleons can determine high-density symmetry energy behavior.

Abstract

The symmetry energy at sub and supra-saturation densities has a great importance in understanding the exact nature of asymmetric nuclear matter as well as neutron star, but, it is poor known, especially at supra-saturation densities. We will demonstrate here that the neutron to proton ratios from different kind of fragments is able to determine the supra-saturation behavior of symmetry energy or not. For this purpose, a series of Sn isotopes are simulated at different incident energies using the Isospin Quantum Molecular Dynamics (IQMD) model with either a soft or a stiff symmetry energy for the present study. It is found that the single neutron to proton ratio from free nucleons as well as LCP's is sensitive towards the symmetry energy, incident energy as well as isospin asymmetry of the system. However, with the double neutron to proton ratio, it 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.