Measurement of |V(cb)| using B̄0 → D*+l-ν̄ decays

Abstract The magnitude of the Cabibbo-Kobayashi-Maskawa matrix element V cb has been measured using B 0 → D ∗+ l − ν decays recorded on the Z 0 peak using the OPAL detector at LEP. The D ∗+ → D 0 π + decays were reconstructed both in the particular decay modes D 0 →K − π + and D 0 →K − π + π 0 and via an inclusive technique. The product of | V cb | and the decay form factor of the B 0 → D ∗+ l − ν transition at zero recoil F (1) was measured to be F (1)|V cb |=(37.1±1.0±2.0)×10 −3 , where the uncertainties are statistical and systematic respectively. By using Heavy Quark Effective Theory calculations for F (1) , a value of |V cb |=(40.7±1.1±2.2±1.6)×10 −3 was obtained, where the third error is due to theoretical uncertainties in the value of F (1) . The branching ratio Br( B 0 →D ∗+ l − ν ) was also measured to be (5.26±0.20±0.46)%.