ICHEP00 770 Determination of the B → D ∗ ℓν Decay Width and |Vcb|

We determine the CKM matrix element |Vcb| using a sample of 3.33 million BB̄ events in the CLEO detector at CESR. We determine the yield of reconstructed B → D∗+lν decays as a function of w = vB · vD∗ , and from this we obtain the differential decay rate dΓ/dw. By extrapolating dΓ/dw to w = 1, the kinematic point at which the D is at rest relative to the B, we extract the product |Vcb|F (1), where F (1) is the form factor at w = 1 and is predicted accurately by theory. We find F (1)|Vcb| = 0.0424±0.0018(stat.)±0.0019(syst.). We also integrate the differential decay rate over w to obtain B(B → D∗+lν) = (5.66 ± 0.29 ± 0.33)%. All results are preliminary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Submitted to XXXth International Conference on High Energy Physics, July 2000, Osaka, Japan