Measurement of (→Dℓ) and determination of |V|

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 | V cb |. From a fit to the differential decay distribution we obtain the rate normalization | V cb | F D (1)=(4.11±0.44±0.52)×10 −2 . Using a theoretical calculation of F D (1), the Cabibbo–Kobayashi–Maskawa matrix element | V cb |=(4.19±0.45±0.53±0.30)×10 −2 is obtained, where the last error comes from the theoretical uncertainty of F D (1). The results are based on a data sample of 10.2fb −1 recorded at the ϒ (4 S ) resonance with the Belle detector at the KEKB e + e − collider.