Neutron skin thickness of 208Pb determined from reaction cross section for proton scattering
Abstract
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 12C scattering on 9Be, 12C, 27Al targets was tested in the incident energy range of 30 E in 400 MeV, and it is found that the model reliably reproduces the σR in 30 E in 100 MeV and 250 E in 400 MeV. [Aim] We determine Rn and the neutron skin thickness R skin of 208 Pb by using high-quality σR data for the p+208 Pb scattering in 30 ≤ E in ≤ 100 MeV. The theoretical 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 σ R in 30 ≤ E in ≤ 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 E in = 30--100 MeV, the experimental σR data can be reproduced by assuming the neutron radius of 208 Pb as Rn = 5.722 0.035 fm. [Conclusion] The present result R skin = 0.278 0.035 fm is in good agreement with the recent PREX-II result of r skin = 0.283 0.071 fm.