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

Abstract

Abstract Electron as well as proton elastic scattering is not able to determine the point proton and point neutron densities, $\rho _\tau (r), (\tau =p,n)$, 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. Previous experiments have not provided $\rho _\tau (r)$ uniquely, but the values of the mean square radii of $\rho _p(r)$, $\langle \, r^2\, \rangle _p$, and of $\rho _n(r)$, $\langle \, r^2\, \rangle _n$, are shown to be determined consistently through the fourth moment of the observed charge density, $\langle \, r^4\, \rangle _c$, in 208Pb. The previous analyses of $(\gamma , \pi ^0)$ and $\bar{p}$-nucleus obtained a similar value of $\langle \, r^2\, \rangle _n$, but they do not yield the experimental value of $\langle \, r^4\, \rangle _c$ observed in electron scattering.