QUARKONIUM DECAY MATRIX-ELEMENTS FROM QUENCHED LATTICE QCD

We calculate the long-distance matrix elements for the decays of the l owest-lying S- and P-wave states of charmonium and bottomonium in quen ched lattice QCD, using a nonrelativistic formulation for the heavy qu arks. (The short-distance coefficients are known from perturbation the ory.) In particular, we present the first calculation from QCD first p rinciples of the color-octet contribution to P-wave decay-a contributi on that is absent in potential models. We also give the relations betw een the lattice matrix elements and their continuum counterparts throu gh one-loop order in perturbation theory.