On the connection between relativistic and nonrelativistic descriptions of quarkonium

We present the set of radial equations associated with a two-particle Dirac Hamiltonian containing a Lorentz-scalar confining potential S and an interaction potential V which transforms like the time component of a four-vector. They were solved for V = 0, S = λγ and zero current masses. It is shown that, in this case, it is possible to obtain practically the same mass spectra in the framework of nonrelativistic quantum mechanics using a wide range of potentials and constituent masses. The contribution of the interaction potential V is briefly discussed. (orig.)