Search for $B^+\rightarrow\tau^+\nu$ decays with hadronic $B$ tags
B. Aubert \fIet al.\fP

We present a search for the decay \btn\ using \bcount $\B\Bbar$ pairs collected at the $\Y4S$ resonance with the \babar\ detector at the SLAC PEP-II $B$ Factory. We select a sample of events with one completely reconstructed tag $B$ in a hadronic decay mode (\btodx), and examine the rest of the event to search for a $\btn$ decay. We identify the $\tau$ lepton in the following modes: $\tautoenunu$, $\tautomununu$, $\tautopinu$ and $\tautopipiznu$. We find a 2.2 $\sigma$ excess in data and measure a branching fraction of $\mathcal{B}(\btn)=( 1.8^{+0.9}_{-0.8}(\mbox{stat.})\pm 0.4(\mbox{bkg. syst.}) \pm 0.2 (\mbox{other syst.})) \times 10^{-4}$. We calculate the product of the $B$ meson decay constant $f_{B}$ and $|\Vub|$ to be $f_{B}\cdot|\Vub| = .3}_{-2.5}(\text{stat.})^{+1.2}_{-1.5}(\text{syst.}))\times10^{-4}$~GeV

© 2008 The American Physical Society.