Radiative leptonic decays of heavy mesons

Abstract

We compute the photon spectrum and the rate for the decays B(D)\ensuremath{\rightarrow}l${\ensuremath{\nu}}_{\mathit{l}}$ \ensuremath{\gamma}. 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\ensuremath{\rightarrow}l\ensuremath{\nu}\ensuremath{\gamma} is small, the radiative decay in the B meson case could be of comparable magnitude or even larger than B\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}. This would affect the determination of ${\mathit{f}}_{\mathit{B}}$ if the \ensuremath{\tau} channel cannot be identified. We obtain theoretical estimates for the photonic rates and discuss their possible experimental implications.