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.
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