Charge-independence-breaking interactions in sd-shell nuclei

Nuclear charge-independence-breaking interactions are studied by analyzing mass differences of isospin multiplets in sd-shell nuclei. It is shown that, being consistent with the results of low-energy NN scattering, the pn interaction is 2-3% more attractive than the like-nucleon interactions, and the one- and two-pion exchange potentials which originate from (π0,π±) mass difference account for about 70% of the observed charge independence breaking, after Coulomb contributions are subtracted. The mass differences of isospin multiplets are well explained by introducing a supplementary phenomenological potential which, together with the pion-exchange potentials, reproduces the 1S0-state scattering length. (author)