The Neutron Skin-Thickness of 208Pb Determined by Electron and Proton Scattering

Electron as well as proton elastic scattering is not able to determine the point proton and point neutron densities, ρτ(r), (τ = p, n), separately. If both scatterings are analyzed consistently, those densities would be determined uniquely, since the two densities are observed by different combinations from each other. The previous experiments did not provide ρτ(r) uniquely, but the values of the mean square radii of ρp(r), 〈 r2 〉p, and of ρn(r), 〈 r2 〉n, are shown to be determined consistently through the fourth moment of the observed charge density, 〈 r4 〉c, in 208Pb. The previous analyses of (γ, π0) and $\bar{p}$-nucleus obtained a similar value of 〈 r2 〉n, but they do not yield the experimental value of 〈 r4 〉c observed in electron scattering.