Centrifugal potential confinement

One expects from lowest-order QCD that the short range part of the potential (which arises mainly from one-gluon exchange) is vector in character. On the other hand, lattice QCD calculations and some flux-tube models indicate that the confining potential is a scalar. The experimental evidence is not conclusive, but is consistent with this picture. If these ideas are correct, then there should not be any appreciable spin-spin splitting in quarkonium states with L > 0 because in such states the wave function is small at short distances because of the centrifugal barrier. Measurements of the spin-spin splitting in L > 0 states therefore provide important tests of QCD-motivated potentials. 

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