Determination of the (B)over-bar -> D(*)l(nu)over-bar decay width and vertical bar V-cb vertical bar
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In the standard model, the charged current of the weak interaction is governed by a unitary quark mixing matrix that also leads to CP violation. Measurement of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements is essential to searches for new physics, either through the structure of the CKM matrix, or a departure from unitarity. We determine the CKM matrix element |V cb | using a sample of 310 6 BB events in the CLEO detector at the Cornell Electron Storage Ring. We determine the yield of reconstructed B 0 D* + and B - D* 0 decays as a function of w, the boost of the D* in the B rest frame, and from this we obtain the differential decay rate d/dw. By extrapolating d/dw to w = 1, the kinematic end point at which the D* is at rest relative to the B, we extract the product |V cb |(1), where (1) is the form factor at w=1. We find |V cb |(1) = 0.04310.0013(stat) 0.0018(syst). We combine |V cb |(1) with theoretical results for (1) to determine |V cb | = 0.04690.0014(stat) 0.0020(syst)0.0018(theor). We also integrate the differential decay rate over w to obtain B(B 0 D * + = (6090.190.40)% and B(B - D* 0 ) = (6.500. 200.43)%. 2003 The American Physical Society.