Search for B^{+}→τ^{+}ν decays with hadronic B tags

We present a search for the decay B+→τ+ν using 383×106 BB̅ pairs collected at the Υ(4S) 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 (B-→D(*)0X-), and examine the rest of the event to search for a B+→τ+ν decay. We identify the τ lepton in the following modes: τ+→e+νν̅ , τ+→μ+νν̅ , τ+→π+ν̅ , and τ+→π+π0ν̅ . We find a 2.2σ excess in data and measure a branching fraction of B(B+→τ+ν)=(1.8-0.8+0.9(stat.)±0.4(bkg. syst.)±0.2(other syst.))×10-4. We calculate the product of the B meson decay constant fB and |Vub| to be fB·|Vub|=(10.1-2.5+2.3(stat.)-1.5+1.2(syst.))×10-4  GeV.