Search for B+→e+νe and B+→μ+νμ decays using hadronic tagging

We present a search for the rare leptonic decays B+ ! e+ν and B+ ! μ+ν, using the full *(4S) data sample of 772 × 106 B ¯B pairs collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. One of the B mesons from the *(4S) ! B ¯B decay is fully reconstructed in a hadronic mode while the recoiling side is analyzed for the signal decay. We find no evidence of a signal in any of the decay modes. Upper limits of the corresponding branching fractions are determined as B(B+ ! e+ν) < 3.4 × 10−6 and B(B+ ! μ+ν) < 2.7 × 10−6 at 90% confidence level.