Difference in proton radii of mirror nuclei as a possible surrogate for the neutron skin

TL;DR

This paper investigates whether differences in charge radii of mirror nuclei can serve as a surrogate for neutron-skin thickness and related neutron star properties, using relativistic energy density functional calculations.

Contribution

The study confirms a strong correlation between mirror nuclei charge radii differences, neutron-skin thickness, and the slope of the symmetry energy across various models.

Findings

Charge radii differences correlate with neutron-skin thickness.

Charge radii differences relate to neutron star radii.

Results support using mirror nuclei as a neutron skin proxy.

Abstract

It has been recently suggested that differences in the charge radii of mirror nuclei are proportional to the neutron-skin thickness of neutron-rich nuclei and to the slope of the symmetry energy $L$ [B.A. Brown Phys. Rev. Lett. 119, 122502 (2017)]. The determination of the neutron skin has important implications for nuclear physics and astrophysics. Although the use of electroweak probes provides a largely model-independent determination of the neutron skin, the experimental challenges are enormous. Thus, the possibility that differences in the charge radii of mirror nuclei may be used as a surrogate for the neutron skin is a welcome alternative. To test the validity of this assumption we perform calculations based on a set of relativistic energy density functionals that span a wide region of values of $L$. Our results confirm that the difference in charge radii of various neutron-deficient nickel isotopes and their corresponding mirror nuclei is indeed strongly correlated to both the neutron-skin thickness and $L$. Moreover, given that various neutron-star properties are also sensitive to $L$, a data-to-data relation emerges between the difference in charge radii of mirror nuclei and the radius of low-mass neutron stars.