Search for B- →μ- ν μ Decays at the Belle Experiment

Abstract

We report the results of a search for the rare, purely leptonic decay B-→μ-ν μ performed with a 711 fb-1 data sample that contains 772×106 BB pairs, collected near the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic B-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of B(B-→μ-νμ)=(6.46±2.22±1.60)×10-7 or a frequentist 90% confidence level interval on the B-→μ-ν μ branching fraction of [2.9,10.7]×10-7.