Proton distribution radii of $^{16-24}$O: signatures of new shell closures and neutron skin

TL;DR

This study measures proton radii in oxygen isotopes, revealing neutron skins and shell closures, and compares results with theoretical models, highlighting the role of tensor interactions.

Contribution

It provides new experimental data on proton radii in $^{16-24}$O and links these to shell closures and neutron skins, supporting ab initio and shell model predictions.

Findings

Thick neutron skins observed in $^{22-24}$O.

Local minima in proton radii at shell closures $N$=14 and 16.

Agreement with ab initio and shell model calculations.

Abstract

The root mean square radii of the proton density distribution in $^{16-24}$O derived from measurements of charge changing cross sections with a carbon target at $\sim$900$A$ MeV together with the matter radii portray thick neutron skin for $^{22 - 24}$O despite $^{22,24}$O being doubly magic. Imprints of the shell closures at $N$ = 14 and 16 are reflected in local minima of their proton radii that provide evidence for the tensor interaction causing them. The radii agree with it ab initio calculations employing the chiral NNLO$_{\mathrm{sat}}$ interaction, though skin thickness predictions are challenged. Shell model predictions agree well with the data.