Spectra of prompt electrons from decays of B+ and B0 mesons and ratio of inclusive semielectronic branching fractions

We present spectra of prompt electrons from decays of neutral and charged B mesons. The results are based on 140 fb−1 of data collected by the Belle detector on the ϒ(4S) resonance at the KEKB e+e− asymmetric collider. We tag ϒ(4S)→BB¯ events by reconstructing a B meson in one of several hadronic decay modes; the semileptonic decay of the other B meson is inferred from the presence of an identified electron. We obtain for charged and neutral B mesons the partial rates of semileptonic decay, to electrons with momentum greater than 0.6GeV/c in the B rest frame, and their ratio b+/b0=1.08±0.05±0.02, where the first and second errors are statistical and systematic, respectively.