Radiative Leptonic Decays of Heavy Mesons

Abstract

We compute the photon spectrum and the rate for the decays $B(D)\to lν_lγ$ These photonic modes constitute a potentially large background for the purely leptonic decays which are used to extract the heavy meson decay constants. While the rate for $D\to l\n\g$ is small, the radiative decay in the $B$ meson case could be of comparable magnitude or even larger than $B\to\m\n$. This would affect the determination of $f_B$ if the $τ$ channel cannot be identified. We obtain theoretical estimates for the photonic rates and disscuss their possible experimental implications.