Radiative corrections and semileptonicBdecays

A prescription for approximating electroweak radiative corrections to weak decays is given. The method is illustrated for {τ}{→}e{ν}{ν}{} and a simplified (structureless) model of B{→}Me{ν}{}, M=D or {π}, where the complete O({α}) corrections are known. Our procedure is shown to provide a proper description of radiation damping near the electron's end-point energy and a reasonable estimate of radiative corrections for much of the spectrum as well as the integrated rate. As a practical application, it is applied to the semileptonic decays B{→}Xe{ν}{} where an exact O({α}) treatment of radiative corrections is very difficult, but an estimate of their effect is important for the extraction of Vub and leptonic branching ratios. We also discuss an 18% enhancement of {Υ}(4S){→}B⁺{B}^{{{-}}}$ relative to ${B}⁰B⁰$ due to large Coulomb corrections near threshold.