BREIT-FERMI INTERACTIONS AND FINE-HYPERFINE SPLITTING IN HEAVY QUARKONIA

The adequacy of using the Breit-Fermi type of interactions for describing the fine hyperfine splittings of heavy quarkonia has been examined critically. A potential model which just about accommodates the trend of the recent data on 1P1 states has been studied. The possibility of including the spin-dependent contributions of a pseudoscalar exchange potential is also considered. It is shown that the choice of the Breit-Fermi form for the spin-dependent interactions severely constrains the generally accepted non-relativistic potential and do not allow enough freedom to fit the recent data on 1P1 levels.