CHARM AND BOTTOM SEMILEPTONIC DECAYS

We review the present status of theoretical attempts to calculate the semileptonic charm and bottom decays and then present a calculation of these decays in the light-front frame at the kinematic point q(2)=0. This allows us to evaluate the form factors at the same value of q(2), even though the allowed kinematic ranges for charm and bottom decays are very different. Also, at this kinematic point the decay is given i n terms of only one form factor A(0)(0). For the ratio. of the decay r ates given by the E653 collaboration we show that the determination of the ratio of the Cabibbo-Kobayashi-Maskawa matrix elements is consist ent with that obtained from the unitarity constraint, though a new mea surement by the E687 Collaboration is about two standard deviations to o high. At present, though, the unitarity method still has greater acc uracy. Since comparisons of the semileptonic decays into rho and eithe r electrons or muons will be available soon from the E791 Fermilab exp eriment, we also look at the massive muon case. We show that for a ran ge of q(2) the SU(3)(F) symmetry breaking is small even though the con tributions of the various helicity amplitudes becomes more complicated . For B decays, the decay B-->Kl (l) over bar at q(2)=0 involves an e xtra form factor coming from the photon contribution and so is not ame nable to the same kind of analysis, leaving only the decay B-->Kv (v) over bar as a possibility. As the mass of the decaying particle incre ases we note that the SU(3) symmetry becomes badly broken at q(2)=0.