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

TL;DR

This study searches for the rare leptonic decay of B- mesons into tau and neutrino, using data from the BaBar detector, but finds no evidence and sets an upper limit on the decay's branching fraction.

Contribution

First search for B- to tau- neutrino decay using BaBar data, establishing an upper limit on its branching fraction.

Findings

No evidence of the decay was observed.

An upper limit on the branching fraction was set at 4.2 x 10^-4.

The analysis constrains theoretical models predicting this decay.

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 $\Upsilon(4S)$ 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.