Constraints on Nuclear Symmetry Energy Parameters

Abstract

A review is made of constraints on the nuclear symmetry energy parameters arising from nuclear binding energy measurements, theoretical chiral effective field predictions of neutron matter properties, the unitary gas conjecture, and measurements of neutron skin thicknesses and dipole polarizabilities. While most studies have been confined to the parameters (Formula presented.) and L, the important roles played by, and constraints on (Formula presented.), or, equivalently, the neutron matter incompressibility (Formula presented.), are discussed. Strong correlations among (Formula presented.), and (Formula presented.) are found from both nuclear binding energies and neutron matter theory. However, these correlations somewhat differ in the two cases, and those from neutron matter theory have smaller uncertainties. To 68% confidence, it is found from neutron matter theory that (Formula presented.) MeV, (Formula presented.) MeV and (Formula presented.) MeV. Theoretical predictions for neutron skin thickness and dipole polarizability measurements of the neutron-rich nuclei (Formula presented.) Ca, (Formula presented.) Sn, and (Formula presented.) Pb are compared to recent experimental measurements, most notably the CREX and PREX neutron skin experiments from Jefferson Laboratory. By themselves, PREX I+II measurements of (Formula presented.) Pb and CREX measurement of (Formula presented.) Ca suggest (Formula presented.) MeV and (Formula presented.) MeV, respectively, to 68% confidence. However, we show that nuclear interactions optimally satisfying both measurements imply (Formula presented.) MeV, nearly the range suggested by either nuclear mass measurements or neutron matter theory, and is also consistent with nuclear dipole polarizability measurements. This small parameter range implies (Formula presented.) km and (Formula presented.), which are consistent with NICER X-ray and LIGO/Virgo gravitational wave observations of neutron stars.