Measurement of the B0-bar -> D*+ l- nu-bar_l decay rate and |Vcb|

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| based on a sample of about 53 700 B0bar -> D*+ l- nubar_l decays observed by the BABAR detector. We obtain the branching fraction averaged over l=e,mu, BR(B0bar -> D*+ l− nubar_l)=(4.90±0.07(stat.)+0.36-0.35(syst.))%. We measure the differential decay rate as a function of w, the relativistic boost γ of the D*+ in the B0bar rest frame. By extrapolating dΓ/dw to the kinematic limit w -> 1, we extract the product of |Vcb| and the axial form factor A1(w=1). We combine this measurement with a lattice QCD calculation of A1(w=1) to determine |Vcb|=(38.7±0.3(stat.)±1.7(syst.)+1.5-1.3(theory))×10-3.