Direct determination of the neutron skin thicknesses in ${}^{40,48}$Ca from proton elastic scattering at $E_p=295$ MeV

Abstract

The neutron density distributions and neutron skin thicknesses in ${}^{40,48}$Ca are determined from the angular distributions of the cross sections and analyzing powers of polarized proton elastic scattering at $E_p=295$ MeV. Based on the framework of the relativistic impulse approximation with the density-dependent effective $NN$ interaction, the experimental data is successfully analyzed, providing precise information of neutron and proton density profiles of ${}^{40,48}$Ca with small uncertainties. The extracted neutron and proton density distributions give neutron skin thicknesses in ${}^{40,48}$Ca for $-0.010_{-0.024}^{+0.022}$ fm and $0.168_{-0.028}^{+0.025}$ fm, respectively. The results of the density profiles and the neutron skin thickness in ${}^{48}$Ca are directly compared with the {\it ab initio} coupled-cluster calculations with interactions derived from chiral effective field theory, as well as relativistic and non-relativistic energy density functional theories.

Comments: 5 pages, 4 figures