Measurement of the inclusive semileptonic branching fraction of B mesons and vertical bar Vcb vertical bar

We present a measurement of the electron spectrum from inclusive semileptonic B decay, using 5.1 fb-1 of Υ(4S) data collected with the Belle detector. A high-momentum lepton tag was used to separate the semileptonic B decay electrons from secondary decay electrons. We obtained the branching fraction, B(B→Xe+ν)=(10.90±0.12±0.49)%, with minimal model dependence. From this measurement, we derive a value for the Cabibbo-Kobayashi-Maskawa matrix element vertical bar Vcb vertical bar =0.0408±0.0010(exp)±0.0025(th)