Determination of |Vcb| using the semileptonic decay B̄0→D∗+e−ν̄

Abstract We present a measurement of the Cabibbo–Kobayashi–Maskawa (CKM) matrix element | V cb | using a 10.2 fb −1 data sample recorded at the ϒ (4S) resonance with the Belle detector at the KEKB asymmetric e + e − storage ring. By extrapolating the differential decay width of the B 0 →D ∗+ e − ν decay to the kinematic limit at which the D ∗+ is at rest with respect to the B 0 , we extract the product of | V cb | with the normalization of the decay form factor F (1), | V cb | F (1)=(3.54±0.19±0.18)×10 −2 , where the first error is statistical and the second is systematic. A value of | V cb |=(3.88±0.21±0.20±0.19)×10 −2 is obtained using a theoretical calculation of F (1), where the third error is due to the theoretical uncertainty in the value of F (1). The branching fraction B ( B 0 →D ∗+ e − ν ) is measured to be (4.59±0.23±0.40)×10 −2 .