Measurement of the Weak Charged Current Structure In Semileptonic B-hadron Decays At the Z-peak

The neutrino energy spectrum in semileptonic b-hadron decays with identified energetic electrons and muons has been measured. The observed relative energy sharing between the neutrino and the charged lepton is found to be well described with a W-+/- polarization obtained from a free b-quark decay model with a (V-A)x(V-A) decay structure. The alternative of a (V+A) x(V-A) decay structure is excluded with a significance of more than 6 standard deviations. The possibility that hadronic corrections to the b-hadron decay destroy any W-+/- polarization is disfavored by more than 3 standard deviations.