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

We present a search for the decay B+->tau(+)nu using 383x10(6) B (B) over bar pairs collected at the Upsilon(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-->(DX-)-X-(*)0), and examine the rest of the event to search for a B+->tau(+)nu decay. We identify the tau lepton in the following modes: tau(+)-> e(+)nunu, tau(+)->mu(+)nu(nu) over bar, tau(+)->pi(+)(nu) over bar, and tau(+)->pi(+)pi(0)(nu) over bar. We find a 2.2 sigma excess in data and measure a branching fraction of B(B+->tau(+)nu)=(1.8(-0.8)(+0.9)(stat.)+/- 0.4(bkg. syst.)+/- 0.2(other syst.))x10(-4). We calculate the product of the B meson decay constant f(B) and [V-ub] to be f(B)center dot[V-ub]=(10.1(-2.5)(+2.3)(stat.)(-1.5)(+1.2)(syst.))x10(-4) GeV.