Neutron skin thickness of Pb 208 determined from the reaction cross section for proton scattering

Background: The reaction cross section σR is useful to determine the neutron radius Rn as well as the matter radius Rm. The chiral (Kyushu) g-matrix folding model for C12 scattering on Be9, C12, Al27 targets was tested in the incident energy range of 30 Ein 400 MeV, and it is found that the model reliably reproduces the σR in 30 Ein 100 MeV and 250 Ein 400 MeV. Purpose: Our aim is to determine rskin208(EXP) from σR(EXP) for p+Pb208 scattering in 30≤Elab≤100 MeV. Methods: Our model is the Kyushu g-matrix folding model with the densities calculated with Gongny-D1S HFB (GHFB) with the angular momentum projection (AMP). Results: The Kyushu g-matrix folding model with the GHFB+AMP densities underestimates σR in 30≤Ein≤100 MeV only by a factor of 0.97. Since the proton radius Rp calculated with GHFB+AMP agrees with the precise experimental data of 5.444 fm, the small deviation of the theoretical result from the data on σR allows us to scale the GHFB+AMP neutron density so as to reproduce the σR data. In Ein=30-100 MeV, the experimental σR data can be reproduced by assuming the neutron radius of Pb208 as Rn=5.722±0.035 fm. Conclusion: The present result Rskin=0.278±0.035 fm is in good agreement with the recent PREX-II result of rskin=0.283±0.071 fm.