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

Abstract

The symmetry energy at sub-and supra-saturation densities has great importance for understanding the exact nature of asymmetric nuclear matter as well as neutron stars, but it is poorly known, especially at supra-saturation densities. We will demonstrate here whether or not the neutron-toproton 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 isospin quantum 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 isospin asymmetry 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.

Constraining the high-density nuclear symmetry energy with the transverse-momentum-dependent elliptic flow

“…Usually, the measured experimental data are compared with corresponding results of microscopic transport models in order to extract the information they carry with regard to properties of the symmetry energy. Several observables have been found or predicted to be sensitive to the nuclear symmetry energy as, e.g., neutron and proton yields and flow ratios, double ratios, or differences, π − / π + and K 0 /K + meson production ratios, the Σ − /Σ + ratio, and the balance energy of directed flow [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. However, even though precise experimental data are available for some of these quantities, their interpretation is strongly model dependent and the obtained constraints on the nuclear symmetry energy at high densities are not consistent with each other (see, e.g., Refs.…”

Effect of neutron skin thickness on projectile fragmentation

“…Therefore, it is interesting to study the effects of neutron skin and symmetry energy separately. The correlations between symmetry energy and the particle or fragment productions have also been investigated in many theoretical studies [32][33][34]. The flexibility of adjusting independently the size of neutron skin of colliding nuclei is useful for our analyses in this work.…”

Isospin Effects on the Transverse Momentum Spectra of Protons and Neutrons

“…The transverse flow of nucleons is also found to be sensitive to symmetry energy as well as to its density dependence in the Fermi energy region [7]. Kumar et al [15] compared theoretical results of single and double neutron to proton ratios with the experimental data and favored the softness of the symmetry energy at sub-saturation densities. At supra-saturation densities, double neutron-to-proton ratio from free nucleons is found to be highly sensitive to the symmetry energy and isospin asymmetry of the system.…”