Spin effects in quarkonia

Abstract

The spin-spin mass splitting leptonic decays of heavy and mixed mesons are described within good accuracy in the potential model with screened potential. We conclude that the long-distance part of the potential cannot be pure scalar and that vector-scalar mixture is favoured. With the same parameters which give correct average mass spectrum excellent spin-spin splittings of heavy quarkonia is obtained. The results are obtained by going beyond usually used perturbation method, namely, using "configuration interaction approach" (CIA). It is known that the first term of CIA method is in fact just a perturbative method result. CIA expansion better takes into account the interaction between particles. The suggested method is of considerable interest, since the perturbation method is still used as the practical method. We turned to use realistic potential, namely, screened potential.