Instantons and Spin Forces between Massive Quarks

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 $\frac{J}{\ensuremath{\psi}}(3100)$ and ${\ensuremath{\eta}}_{c}(2830)$ 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.

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