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

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.

5 pages, 4 figures, accepted for publication in Phys. Rev. Lett