Neutron skins: A perspective from dispersive optical models

An overview is presented of neutron skin predictions obtained using an empirical nonlocal dispersive optical model (DOM). The DOM links both scattering and bound-state experimental data through a subtracted dispersion relation which allows for fully-consistent, data-informed predictions for nuclei where such data exists. Large skins were predicted for both ^48Ca (R^48ₛkin=0. 25 0. 023 fm in 2017) and ^208Pb (R^208ₛkin=0. 25 0. 05 fm in 2020). While the DOM prediction in ^208Pb is within 1 of the subsequent PREX-2 measurement, the DOM prediction in ^48Ca is over 2 larger than the thin neutron skin resulting from CREX. From the moment it was revealed, the thin skin in ^48Ca has puzzled the nuclear-physics community as no adequate theories simultaneously predict both a large skin in ^208Pb and a small skin in ^48Ca. The DOM is unique in its ability to treat both structure and reaction data on the same footing, providing a unique perspective on this Rₛkin puzzle. It appears vital that more neutron data be measured in both the scattering and bound-state domain for ^48Ca to clarify the situation.