Search for B⁺ → e⁺ν_e and B⁺ → μ⁺ν_μ decays using hadronic tagging

We present a search for the rare leptonic decays B⁺ → e⁺ν_e and B⁺ → μ⁺ν_μ, using the full Υ(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 Υ(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_e) < 3.5 × 10^-6 and B(B⁺ → μ⁺ν_μ) < 2.7 × 10^-6 at 90% confidence level.