Evidence of B[superscript +]→τ[superscript +]ν decays with hadronic B tags

Abstract

We present a search for the decay B[superscript +]→τ[superscript +]ν using 467.8×10[superscript 6] 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 B[superscript -] in the hadronic decay mode (B[superscript -]→D[superscript (*)0]X[superscript -] and B[superscript -]→J/ψX[superscript -]). We examine the rest of the event to search for a B[superscript +]→τ[superscript +]ν decay. We identify the τ[superscript +] lepton in the following modes: τ[superscript +]→e[superscript +]νν̅ , τ[superscript +]→μ[superscript +]νν̅ , τ[superscript +]→π[superscript +]ν̅ and τ[superscript +]→ρ[superscript +]ν̅ . We find an excess of events with respect to the expected background, which excludes the null signal hypothesis at the level of 3.8σ (including systematic uncertainties) and corresponds to a branching fraction value of B(B[superscript +]→τ[superscript +]ν)=(1.83[+0.53 over -0.49](stat)±0.24(syst))×10[superscript -4].