A search for B+ --> tau+ nu with Hadronic B tags

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We present a search for the decay B+ --> tau+ nu using 383 × 10⁶ BBbar 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- → D⁽*⁾⁰ X-), 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+ nu nu,tau+ --> mu+ nu nu, tau+ --> pi+ nu and tau+ --> pi+ pi⁰ nu. We find a 2.2 sigma excess in data and measure a branching fraction of B(B+ --> tau+ nu) = (1.8⁺⁰.⁹₋₀.₈(stat.) ± 0.4(bkg. syst.) ± 0.2 (other syst.)) × 10⁴. We calculate the product of the B meson decay constant fB and |Vub| to be fB |Vub| = (10.1⁺².³₋₂.₅(stat.)⁺¹.²₋₁.₅(syst.))×10⁻⁴ GeV