Determination Of The (B)Over-Bar -> D(*)L(Nu)Over-Bar Decay Width And Vertical Bar V-Cb Vertical Bar

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 3x10(6) B (B) over bar events in the CLEO detector at the Cornell Electron Storage Ring. We determine the yield of reconstructed (B) over bar (0)-->D*(+)l (ν) over bar and B--->D(*0)l (ν) over bar 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 dGamma/dw. By extrapolating dGamma/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\F(1), where F(1) is the form factor at w=1. We find \V-cb\F(1)=0.0431+/-0.0013(stat)+/-0.0018(syst). We combine \V-cb\F(1) with theoretical results for F(1) to determine \V-cb\=0.0469+/-0.0014(stat)+/-0.0020(syst)+/-0.0018(theor). We also integrate the differential decay rate over w to obtain B((B) over bar (0)-->D*(+)(ν) over bar)=(6.09+/-0.19+/-0.40)% and B(B--->D*(0)l (ν) over bar)=(6.50+/-0.20+/-0.43)%.