Tight Symmetry Energy Parameter Constraints from Neutron Skin Measurements

Inferences of nuclear symmetry energy parameters from recent parity-violating neutron skin measurements of the neutron-rich nuclei Ca-48 and Pb-208 appear to be in tension with each other and values obtained from fitting either nuclear masses or neutron matter theory. By themselves, PREX I+II measurements of Pb-208 and CREX measurements of Ca-48 suggest L≃110±36 MeV and L≃23±27 MeV, respectively, to 68% confidence. However, jointly satisfying both at 90% confidence implies L≃51±11MeV, nearly exactly the range suggested by nuclear mass fitting or neutron matter theory. This small inferred parameter range is also consistent with nuclear dipole polarizability measurements and X-ray and gravitational wave observations of neutron stars.