Search for B+ -> l(+)nu(l) recoiling against B- -> D(0)l(-)(nu)over-barX

We present a search for the decay B+→ℓ+νℓ(ℓ=τ,μ, or e) in (458.9±5.1)×106 BB⎯⎯⎯ pairs recorded with the BABAR detector at the PEP-II B-factory. We search for these B decays in a sample of B+B− events where one B-meson is reconstructed as B−→D0ℓ−ν⎯⎯X. Using the method of Feldman and Cousins, we obtain ℬ(B+→τ+ντ)=(1.7±0.8±0.2)×10−4, which excludes zero at 2.3σ. We interpret the central value in the context of the standard model and find the B meson decay constant to be f2B=(62±31)×103  MeV2. We find no evidence for B+→e+νe and B+→μ+νμ and set upper limits at the 90% C.L. ℬ(B+→e+νe)<0.8×10−5 and ℬ(B+→μ+νμ)<1.1×10−5.