A Measurement of $|Vcb|$ from $\overline B^{0} \to D^{*} + l-\overline{\nu}_l$

From approximately 3 million hadronic decays of Z bosons recorded with the ALEPH detector at LEP, a sample of 410 +/- 32 B0bar -> D*+ l- nubar candidates is selected, where l- is either an electron or a muon. The differential decay rate dGamma(B0bar -> D*+ l- nubar)/dw from this sample is fitted, yielding a value for the product of the CKM matrix element |Vcb| and the normalisation of the decay form factor at the point of zero recoil of the D*+ meson: F(w=1)|Vcb| = [31.4 +/-2.3(stat.) +/-2.5(syst.)] #users.txt# DistList LAforwarding PSforwarding batch done errors files helpND.html images insert_new.sh instlog log modifying pending pending.bk running stats users.txt users.txt~ waiting 10^(-3). A value for |Vcb| is extracted using theoretical calculations of the form factor normalisation, with the result: |Vcb| = [34.5 +/-2.5(stat.) +/-2.7(syst.) +/-1.5(theory)] #users.txt# DistList LAforwarding PSforwarding batch done errors files helpND.html images insert_new.sh instlog log modifying pending pending.bk running stats users.txt users.txt~ waiting 10^(-3). From the integrated spectrum, the measured branching fraction is Br(B0bar -> D*+ l- nubar) = 5.18 +/-0.30(stat.) +/-0.62(syst.)%.