A Search for $B\to \tau\nu$

TL;DR

This paper reports a search for the rare decay $B\to \tau\nu$ using a large data sample, setting upper limits on its branching fraction and also on $B^\pm\to K^\pm\nu\bar\nu$, contributing to understanding of B meson decays.

Contribution

First to set experimental upper limits on $B\to \tau\nu$ and $B^\pm\to K^\pm\nu\bar\nu$ branching fractions using exclusive reconstruction methods.

Findings

Upper limit on $B\to \tau\nu$ branching fraction: $8.4\times 10^{-4}$

Upper limit on $B^\pm\to K^\pm\nu\bar\nu$ branching fraction: $2.4\times 10^{-4}$

Used 9.7 million charged B meson decays for analysis.

Abstract

We report results of a search for $B\to\tau\nu$ in a sample of 9.7 million charged $B$ meson decays. The search uses both $\pi\nu$ and $\ell\nu\bar\nu$ decay modes of the $\tau$, and demands exclusive reconstruction of the companion $\bar B$ decay to suppress background. We set an upper limit on the branching fraction ${\cal B}(B\to \tau\nu) < 8.4\times 10^{-4}$ at 90% confidence level. With slight modification to the analysis we also establish ${\cal B}(B^\pm\to K^\pm\nu\bar\nu) < 2.4\times 10^{-4}$ at 90% confidence level.