Quark models of nuclear isobaric energy differences

Abstract

We study the energy differences between mirror nuclei in both nonrelativistic (NR) and relativistic quark models based on the one-gluon exchange interaction. Both six-quark (6q) and resonating-group (RG) methods are used to treat the effects of overlapping nucleons in nuclei. The 6q method is simple and useful, but it can give only qualitative results because of a lack of precision and the neglect of non-(1s)6 configurations. It is used here to compare bag and potential models of quarks and to study the effects of kinetic energy, quark-quark interaction and nucleon size. Six-quark results show that the usual Breit-Fermi NR reduction has serious limitations in treating quark masses and nucleon sizes. In contrast, the RG method is much more complete, but it is also much harder to use. It is used here with simple NR potential models to study the effects of complicated 6q configurations, nucleon size and nucleon-nucleon short-range correlations. We find that NR potential models tend to give Nolan-Schiffer anomalies larger than experimental results, while bag models give too small results, especially if the bag radius is as small as 0.6 fm.