Constraints on the Symmetry Energy from PREX-II in the Multimessenger Era

TL;DR

This paper constrains the symmetry energy slope parameter using PREX-II neutron skin data, finite nuclei properties, heavy-ion collision data, and neutron star observations, narrowing the range of possible symmetry energy behaviors.

Contribution

It provides a combined analysis of nuclear and astrophysical data to tightly constrain the symmetry energy slope parameter at sub-saturation density.

Findings

The symmetry energy slope at 2/3 saturation density is between 52 and 73 MeV.

The neutron skin thickness of Pb-208 is between 0.212 and 0.271 fm.

Symmetry energy at saturation density is approximately 34.3 MeV.

Abstract

The neutron skin thickness $\Delta r_{\rm{np}}$ of heavy nuclei is essentially determined by the symmetry energy density slope $L({\rho })$ at $\rho_c = 0.11~{\rm {fm}^{-3}}\approx 2/3\rho_0$ ($\rho_0$ is nuclear saturation density), roughly corresponding to the average density of finite nuclei. The PREX collaboration recently reported a model-independent extraction of $\Delta r^{208}_{\rm{np}} = 0.283 \pm 0.071$ fm for the $\Delta r_{\rm{np}}$ of $^{208}$Pb, suggesting a rather stiff symmetry energy $E_{\rm{sym}}({\rho })$ with $L({\rho_c }) \ge 52$ MeV. We show that the $E_{\rm{sym}}({\rho })$ cannot be too stiff and $L({\rho_c }) \le 73$ MeV is necessary to be compatible with (1) the ground-state properties and giant monopole resonances of finite nuclei, (2) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, (3) the largest neutron star (NS) mass reported so far for PSR J0740+6620, (4) the NS tidal deformability extracted from gravitational wave signal GW170817 and (5) the mass-radius of PSR J0030+045 measured simultaneously by NICER. This allows us to obtain $52 \le L({\rho_c }) \le 73$ MeV and $0.212 \le \Delta r^{208}_{\rm{np}} \le 0.271$ fm, and further $E_{\rm{sym}}({\rho_0 }) = 34.3 \pm 1.7$ MeV, $L({\rho_0 }) = 83.1 \pm 24.7$ MeV, and $E_{\rm{sym}}({2\rho_0 }) = 62.8 \pm 15.9$ MeV. A number of critical implications on nuclear physics and astrophysics are discussed.