Neutron skin of $^{48}$Ca consistent with experimental data on skins

Abstract

[Background]: In our previous paper, we predicted $r_{\rm skin}$, $r_{\rm p}$, $r_{\rm n}$, $r_{\rm m}$ for $^{40-60,62,64}$Ca after determining the neutron dripline, using the Gogny-D1S HFB with and without the angular momentum projection (AMP). We found that effects of the AMP are small. Very lately, Tanaka {\it et al.} measured interaction cross sections $\sigma_{\rm I}$ for $^{42-51}$Ca, determined $r_{\rm m}$ from the $\sigma_{\rm I}$, and deduced skin $r_{\rm skin}$ and $r_{\rm n}$ from the $r_{\rm m}$ and the $r_{\rm p}(\rm {exp})$ evaluated from the electron scattering. Comparing our results with the data, we find for $^{42-48}$Ca that GHFB and GHFB+AMP reproduce the data on $r_{\rm skin}$, $r_{\rm n}$, $r_{\rm m}$, but not for $r_{\rm p}(\rm {exp})$. [Aim]: Our purpose is to determine a value of $r_{\rm skin}^{48}$ by using GHFB+AMP and the constrained GHFB (cGHFB) in which the calculated value is fitted to $r_{\rm p}(\rm {exp})$. [Results]: For $^{42,44,46,48}$Ca, cGHFB hardly changes $r_{\rm skin}$, $r_{\rm m}$, $r_{\rm n}$ calculated with GHFB+AMP, except for $r_{\rm skin}^{48}$. For $r_{\rm skin}^{48}$, the cGHFB result is $r_{\rm skin}^{48}=0.190$fm, while $r_{\rm skin}^{48}=0.159$fm for GHFB+AMP. We should take the upper and the lower bound of GHFB+AMP and cGHFB. The result $r_{\rm skin}^{48}=0.159-0.190$fm consists with the $r_{\rm skin}^{48}(\sigma_{\rm I})$ and the data $r_{\rm skin}^{48}(\rm $E1$pE)$ obtained from high-resolution $E1$ polarizability experiment ($E1$pE). Using the $r_{\rm skin}^{48}$-$r_{\rm skin}^{208}$ relation with strong correlation of Ref.[3], we transform the data $r_{\rm skin}^{208}$ determined by PREX and $E1$pE to the corresponding values, $r_{\rm skin}^{48}(\rm tPREX)$ and $r_{\rm skin}^{48}(\rm t$E1$pE)$. Our result is consistent also for $r_{\rm skin}^{48}(\rm tPREX)$ and $r_{\rm skin}^{48}(\rm t$E1$pE)$.