Neutron skin impurity from Coulomb core-polarization in ^208Pb: Insights from PREX-II and validation via (^3He, t) IAS reaction

We investigate the impurity in the neutron skin induced by Coulomb core-polarization, highlighting its impact on uncertainties in neutron skin measurements from PREX-II. This effect is validated using the (^3He, t) IAS reaction at 420 MeV. Our findings reveal that the Coulomb boundary radius, where core-polarization becomes negligible, is critical for accurately probing the neutron skin in the target nucleus. Notably, the (^3He, t) IAS experiment conducted by Zegers et al. Phys. Rev. Lett. 99, 202501 (2007) primarily detects neutron excess at zero scattering angle due to the core-polarization phenomenon, rather than the neutron skin. We propose extending this experiment to measure cross sections at a 3^ angle to more precisely determine the neutron skin thickness in ^208Pb. Additionally, uncertainties in PREX-II may arise from electrons initially probing neutron excess instead of the neutron skin, potentially leading to an overestimation of neutron skin thickness due to the mixing effect where protons are displaced into the neutron skin region.