Measurement of B(Bo - D+Í- v) and determination of | vCb |

Abstract We present a measurement of the branching fraction for the semileptonic B decay B 0 →D + l − ν , where l− can be either an electron or a muon. We find Γ( B 0 →D + l − ν )=(13.79±0.76±2.51)  ns −1 , and the resulting branching fraction B ( B 0 →D + l − ν )=(2.13±0.12±0.39)% , where the first error is statistical and the second systematic. We also investigate the B 0 →D + l − ν form factor and the implications of the result for |Vcb|. From a fit to the differential decay distribution we obtain the rate normalization |Vcb|FD(1)=(4.11±0.44±0.52)×10−2. Using a theoretical calculation of FD(1), the Cabibbo–Kobayashi–Maskawa matrix element |Vcb|=(4.19±0.45±0.53±0.30)×10−2 is obtained, where the last error comes from the theoretical uncertainty of FD(1). The results are based on a data sample of 10.2fb−1 recorded at the ϒ(4S) resonance with the Belle detector at the KEKB e+e− collider.