Measurement of the decays B and B in fully reconstructed events at Belle

We report branching fraction measurements of the decays B+ and B+ based on 711 fb-1 of data collected near the (4S) resonance with the Belle experiment at the KEKB asymmetric-energy e+e- collider. This data sample contains 772 million BB events. One of the two B mesons is fully reconstructed in a hadronic decay mode. Among the remaining ("signal-B") daughters, we search for the η meson in two decay channels, η→γγ and η→π+π-π0, and reconstruct the η′ meson in η′→ηπ+π- with subsequent decay of the η into γγ. Combining the two η modes and using an extended maximum likelihood, the B+ branching fraction is measured to be (4.2±1.1(stat.)±0.3(syst.))×10-5. For B+, we observe no significant signal and set an upper limit of 0.72×10-4 at 90% confidence level.