Neutron skin deduced from antiprotonic atom data

The relationship between the nucleon density at large radii and the value of the rms radius is investigated in the framework of Skyrme Hartree-Fock and relativistic mean-field models. From a comparison to the charge density we constrain the models in terms of the nuclear matter incompressibility and effective mass properties required to reproduce the density shape. The results are used to extract the rms neutron radius for ²⁰⁸Pb from antiprotonic atom data. The result for the difference between the neutron and proton rms radii, the so-called neutron-skin thickness, is S=0.20(±0.04)(±0.05) fm, where ±0.04 fm is experimental error from the antiprotonic line width, and ±0.05 fm is the theoretical error suggested from the comparison of the models with the experimental charge density.