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 = 0. This allows us to evaluate the form factors at the same value of q, even though the allowed kinematic ranges for charm and bottom decays are very different. Also, at this kinematic point the decay is given in terms of only one form factor A0(0). For the ratio of the decay rates given by the E653 collaboration we show that the determination of the ratio of the Cabibbo– Kobayashi–Maskawa (CKM) matrix elements is consistent with that obtained from the unitarity constraint. At present, though, the unitarity method still has greater accuracy. For B decays, the decay B → Kll̄ at q = 0 involves an extra form factor coming from the photon contribution and so is not amenable to the same kind of analysis, leaving only the decay B → Kνν̄ as a possibility. As the mass of the decaying particle increases we note that the SU(3) symmetry becomes badly broken at q = 0.