Constraining neutron skin impurity in ${}^{48}\mathrm{Ca}$ and its relevance for the CREX-PREX puzzle

Abstract

The impact of Coulomb core polarization on the neutron density distribution of ${}^{48}\mathrm{Ca}$ is investigated. The Coulomb boundary radius is located before the neutron skin region, leading to proton admixture and establishing neutron skin impurity as an intrinsic feature of the density profile. Using the ${(}^3\mathrm{He},t)$ isobaric analog state (IAS) reaction at 420 MeV, the impurity-induced modification of the probed neutron distribution is quantified. For a neutron skin of 0.144 fm, consistent with the CREX thin-skin scenario, Coulomb core polarization enhances the probed neutron distribution by approximately 0.052 fm. This value is remarkably close to the difference between the CREX and RCNP neutron skin determinations, providing a physical mechanism to reconcile the discrepancy between electroweak and hadronic probes in ${}^{48}\mathrm{Ca}$. These findings provide new insights into the CREX-PREX puzzle, highlight the importance of accounting for Coulomb core polarization in neutron distribution analyses, and motivate future IAS charge-exchange measurements as a complementary hadronic probe.

Comments: 6 pages, 4 figures. Accepted for publication as a Letter in Physical Review C