Determination of Vcb using the semileptonic decay

We present a measurement of the Cabibbo–Kobayashi–Maskawa (CKM) matrix element |Vcb| 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 B̄0→D∗+e−ν̄ decay to the kinematic limit at which the D∗+ is at rest with respect to the B̄0, we extract the product of |Vcb| with the normalization of the decay form factor F(1), |Vcb|F(1)=(3.54±0.19±0.18)×10−2, where the first error is statistical and the second is systematic. A value of |Vcb|=(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(B̄0→D∗+e−ν̄) is measured to be (4.59±0.23±0.40)×10−2.