The Instantaneous Breit Equation with an Application to Charmonium

The solution of the Breit equation with an instantaneous potential for the case of two spin-1/2 particles in a pseudoscalar bound state is considered. This is then applied to charmonium using a potential of the Cornell type. The masses of the two JP = 0^- states below charm threshold are calculated in this model. We allow different mixtures of the Lorentz nature (vector or scalar) of the linear confining term and investigate the effect of these on the bound-state energies. Some general comments are made on the issue of how the bound nature of these states depends on the vector-scalar mix.