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Electric dipole polarizability and the neutron skin

The recent high-resolution measurement of the electric dipole (E1) polarizability αD in 208Pb [ A. Tamii et al. Phys. Rev. Lett. 107 062502 (2011)] provides a unique constraint on the neutron-skin thickness of this nucleus. The neutron-skin thickness rskin of 208Pb is a quantity of critical importance for our understanding of a variety of nuclear and astrophysical phenomena. To assess the model dependence of the correlation between αD and rskin, we carry out systematic calculations for 208Pb, 132Sn, and 48Ca based on the nuclear density functional theory using both nonrelativistic and relativistic energy density functionals. Our analysis indicates that whereas individual models exhibit a linear dependence between αD and rskin, this correlation is not universal when one combines predictions from a host of different models. By averaging over these model predictions, we provide estimates with associated systematic errors for rskin and αD for the nuclei under consideration. We conclude that precise measurements of rskin in both 48Ca and 208Pb—combined with the recent measurement of αD—should significantly constrain the isovector sector of the nuclear energy density functional.

Neutron skin; Electric dipole polarizability; Nuclear Energy Density Functional

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