The Electron spectrum from B meson decays

The Crystal Ball Collaboration has measured the energy spectrum of electrons from semileptonicB meson decays at thee + e − storage ring DORIS II. Branching ratios and weak mixing angles of the Kobayashi-Maskawa matrix are determined using several models for the hadronic matrix elements. We obtain the branching ratio for semileptonic.B decays to charmed states BR(B→evX c )=(11.7±0.4±1.0)%. Our result for the corresponding Kobayashi-Maskawa matrix element is |V cb |=0.052±0.006. The model dependence of both results is included in the error. We have not observed semileptonicB decays to non-charmed mesons. Analyzing the measured electron spectrum above 2.4 GeV, where nob→c decays contribute, we find BR(B→evX u )/BR(B→evX c )