Instantons and Spin Forces between Massive Quarks

Abstract

A generalization of Wilson's loop prescription to include spin is proposed. Instantons are shown to generate a spin-spin interaction between quarks. The large splitting between $\frac{J}{\psi }\mathrm{}\left(3100\right)\mathrm{}$ and ${\eta }_c\mathrm{}\left(2830\right)\mathrm{}$ may, in fact, be dominated by this mechanism and thus may provide a vivid demonstration of the physical effects of instantons. Heuristic arguments are presented which explain the sign and form of the interaction.