| Abstract |
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We present a search for the decay $B^{+} \rightarrow \tau^{+} \nu_{\tau}$
in $124.1 \times 10^{6}$ $\Upsilon(4S)$ decays recorded with the
$BABAR$ detector at the SLAC PEP-II $B$-Factory.
A sample of events with one reconstructed
exclusive semi-leptonic $B$ decay
($B^- \rightarrow D^{*0} \ell^- \overline{\nu}_{\ell}$)
is selected, and in the recoil a search for
$B^{+} \rightarrow \tau^{+} \nu_{\tau}$ signal is performed. The $\tau$ is
identified in the following channels:
$\tau^+ \to e^+ \nu_e \overline{\nu}_{\tau}$,
$\tau^+ \to \mu^+ \nu_{\mu} \overline{\nu}_{\tau}$,
$\tau^+ \to \pi^+ \overline{\nu}_{\tau}$,
$\tau^+ \to \pi^+ \pi^{0} \overline{\nu}_{\tau}$,
$\tau^+ \to \pi^+ \pi^{-} \pi^{+} \overline{\nu}_{\tau}$.
We find no evidence of signal, and we set a preliminary upper limit
on the branching fraction of
$\mathcal{B}(B^{+} \rightarrow \tau^{+} \nu_{\tau}) < 4.3 \times 10^{-4}$
at the 90\% confidence level (CL). This result is then combined with
a statistically independent $BABAR$
search for $B^{+} \rightarrow \tau^{+} \nu_{\tau}$
to give a combined preliminary limit of
$\mathcal{B}(B^{+} \rightarrow \tau^{+} \nu_{\tau}) < 3.3 \times 10^{-4}$
at 90\% CL.
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