A Search for B+ --> tau+ nu Recoiling Against B- --> D0 l- nu X

Abstract

We present a search for the decay $B^{+} \to τ^{+} ν_τ$ in $88.9 \times 10^{6}$ $Υ(4S)$ decays recorded with the BABAR detector at the SLAC $B$-Factory. A sample of semi-exclusive, semi-leptonic B decays ($B^{-} \to D^{0} \ell^{-} \bar{ν_{\ell}}X$), where $X$ is either a photon, $π^{0}$, or nothing, is used to identify the daughter particles that are associated with the other $B$ meson in each event. These particles are searched for evidence of a one-prong leptonic $B^{+} \to τ^{+} ν_τ$ decay. For this data sample we set a preliminary upper limit on the branching fraction of $\mathcal{B}(B^{+} \to τ^{+} ν_τ) < 4.9 \times 10^{-4}$ at the 90% confidence level. This result is then combined with a statistically independent BABAR search for $B^{+} \to τ^{+} ν_τ$ to give a combined preliminary limit of $\mathcal{B}(B^{+} \to τ^{+} ν_τ) < 4.1 \times 10^{-4}$.