Complete electric dipole response and the neutron skin in Pb208

A benchmark experiment on Pb208 shows that polarized proton inelastic scattering at very forward angles including 0° is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r skin=0.156-0.021+0.025fm in Pb208 derived within a mean-field model, thereby constraining the symmetry energy and its density dependence relevant to the description of neutron stars. © 2011 American Physical Society.