Search for the decay $B^{+}\to {\tau }^{+}{\nu }_{\tau }$

We search for the rare leptonic decay $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ in a sample of $232\times {10}^6$ $B\overline{B}$ pairs collected with the BABAR detector at the SLAC PEP-II $B$-Factory. Signal events are selected by examining the properties of the $B$ meson recoiling against the semileptonic decay $B^{-}\to D^{*0}{\ell }^{-}{\overline{\nu }}_{\ell }$. We find no evidence for a signal and set an upper limit on the branching fraction of $\mathcal{B}(B^{+}\to {\tau }^{+}{\nu }_{\tau })<2.8\times {10}^{-4}$ at the 90% confidence level. We combine this result with a previous, statistically independent BABAR search for $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ to give an upper limit of $\mathcal{B}(B^{+}\to {\tau }^{+}{\nu }_{\tau })<2.6\times {10}^{-4}$ at the 90% confidence level.

Figure 1

The distribution of $E_{\mathrm{extra}}$ after applying all other selection criteria, plotted for (a) $e^{+}{\nu }_e{\overline{\nu }}_{\tau }$, (b) ${\mu }^{+}{\nu }_{\mu }{\overline{\nu }}_{\tau }$, (c) ${\pi }^{+}{\overline{\nu }}_{\tau }$, (d) misidentified lepton, (e) ${\pi }^{+}{\pi }^0{\overline{\nu }}_{\tau }$, and (f) ${\pi }^{+}{\pi }^{-}{\pi }^{+}{\overline{\nu }}_{\tau }$ channels. The data and background MC samples are represented by the points with error bars and solid histograms, respectively. The dotted lines indicate the $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ signal distribution from MC. The signal MC events for the $e^{+}{\nu }_e{\overline{\nu }}_{\tau }$, ${\mu }^{+}{\nu }_{\mu }{\overline{\nu }}_{\tau }$, ${\pi }^{+}{\overline{\nu }}_{\tau }$, and misidentified-lepton (${\pi }^{+}{\pi }^0{\overline{\nu }}_{\tau }$ and ${\pi }^{+}{\pi }^{-}{\pi }^{+}{\overline{\nu }}_{\tau }$) channels are normalized assuming a branching fraction of ${10}^{-3}$ (${10}^{-2}$) for $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ decay.