Proton distribution radii of $^{12-19}$C illuminate features of neutron halos

TL;DR

This study measures proton radii of carbon isotopes from $^{12}$C to $^{19}$C, revealing neutron surface evolution and halo features, with results supported by ab initio theoretical calculations.

Contribution

It provides the first accurate charge-changing cross section measurements for these isotopes and links experimental data with advanced ab initio models.

Findings

Neutron surface extends from 0.5 fm in $^{15}$C to 1 fm in $^{19}$C.

Halo radius in $^{19}$C is approximately 6.4 fm, comparable to $^{11}$Li.

Ab initio calculations successfully reproduce measured radii.

Abstract

Proton radii of $^{12-19}$C densities derived from first accurate charge changing cross section measurements at 900$A$ MeV with a carbon target are reported. A thick neutron surface evolves from $\sim$ 0.5 fm in $^{15}$C to $\sim$ 1 fm in $^{19}$C. The halo radius in $^{19}$C is found to be 6.4$\pm$0.7 fm as large as $^{11}$Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce well the radii.