Electric dipole polarizability of $^{48}$Ca and implications for the neutron skin

TL;DR

This study measures the electric dipole polarizability of calcium-48 using proton scattering and photoabsorption data, providing insights into its neutron skin thickness and confirming theoretical predictions.

Contribution

First extraction of electric dipole polarizability of Ca-48 combining scattering and absorption data, linking it to neutron skin thickness and validating theoretical models.

Findings

Alpha_D(Ca-48) = 2.07(22) fm^3

Neutron skin thickness estimated at 0.14-0.20 fm

Dipole response similar to Ca-40

Abstract

The electric dipole strength distribution in Ca-48 between 5 and 25 MeV has been determined at RCNP, Osaka, from proton inelastic scattering experiments at forward angles. Combined with photoabsorption data at higher excitation energy, this enables for the first time the extraction of the electric dipole polarizability alpha_D(Ca-48) = 2.07(22) fm^3. Remarkably, the dipole response of Ca-48 is found to be very similar to that of Ca-40, consistent with a small neutron skin in Ca-48. The experimental results are in good agreement with ab initio calculations based on chiral effective field theory interactions and with state-of-the-art density-functional calculations, implying a neutron skin in Ca-48 of 0.14 - 0.20 fm.