CHARMONIUM IN THE INSTANTANEOUS APPROXIMATION

The charmonium system is studied in a Salpeter model with a vector plu s scalar potential. We use a kinematical formalism based on the one de veloped by Suttorp, and present general eigenvalue equations and expre ssions for decay observables in an onium system for such a potential b oth in the Feynman and Coulomb gauges. Special attention is paid to th e problem with renormalization of the lepton pair decays, and we argue that they must be defined relative to one of the experimental decay w idths because renormalization of the vertex function is not possible. The parameters of the model are determined by a fit to the mass spectr um and the lepton pair decay rates. Two gamma decays and E1 and M1 tra nsitions are then calculated and found to be well accounted for. No si gnificant differences in the results in Feynman or Coulomb gauge are f ound. A comparison is made, regarding the electromagnetic transitions, between the full and reduced Salpeter equation. A large difference is found showing the importance of using the full Salpeter equation. (C) 1997 Elsevier Science B.V.