THE HYPERFINE SPLITTING IN CHARMONIUM - LATTICE COMPUTATIONS USING THE WILSON AND CLOVER FERMION ACTIONS

We compute the hyperfine splitting m(J/psi)-m(etac) on the lattice, using both the Wilson and O(a)-improved (clover) actions for quenched quarks. The computations are performed on a 24(3)x48 lattice at beta=6.2, using the same set of 18 gluon configurations for both fermion actions. We find that the splitting is 1.83(-15)+13 times larger with the clover action than with the Wilson action, demonstrating the sensitivity of the spin-splitting to the magnetic moment term which is present in the clover action. However, even with the clover action the result is less than half of the physical mass-splitting. We also compute the decay constants f(etac) and f(J/psi)-1, both of which are considerably larger when computed using the clover action than with the Wilson action. For example for the ratio f(J/psi)-1/f(rho)-1 we find 0.32(-2)+1 with the Wilson action and 0.48+/-3 with the clover action (the physical value is 0.44(2)).