Search for the Rare Leptonic Decay B- -> tau- nubar

Abstract

We present a search for the decay $B^{-}\to {\tau }^{-}{\bar{\nu }}_{\tau }$ in a sample of $88.9\times 10^6$ $B\bar{B}$ pairs recorded with the BaBar detector at the SLAC $B$-Factory. One of the two $B$ mesons from the ${\rm Y}(4S)$ is reconstructed in a hadronic or a semileptonic final state and the decay products of the other $B$ in the event are analyzed for consistency with a $B^{-}\to {\tau }^{-}{\bar{\nu }}_{\tau }$ decay. We find no evidence of a signal and set an upper limit on the branching fraction of $\mathcal{B}(B^{-}\to {\tau }^{-}{\bar{\nu }}_{\tau })<4.2\times 10^{-4}$ at the 90% confidence level.

7 pages, 2 figures, Submitted to Physical Review Letters