A search for the decays $B^+\to e^+ ν_e$ and $B^+\to μ^+ ν_μ$ using hadronic-tag reconstruction

Abstract

We report on a search for the rare decay modes $B^+\to e^+ ν_e$ and $B^+\to μ^+ ν_μ$ with data collected from the BaBar detector at the PEP-II $e^+e^-$ storage ring. This search utilizes a new technique in which we fully reconstruct the accompanying $B^-$ in $Υ(4S)\righarrow B^+ B^-$ events, and look for a mono-energetic lepton in the $B^+$ rest frame. No signal candidates are observed in either of the channels, consistent with the expected background, in a data sample of approximately 229 million $B\bar{B}$ pairs. The branching-fraction upper limits are set at $\mathcal{B}(B^+\to e^+ν_{e})<7.9 \times 10^{-6}$ and $\mathcal{B}(B^+\toμ^+ν_μ)<6.2 \times 10^{-6}$ at the 90% confidence level.