Measurement of the Λb polarization in Z decays

Abstract The Λ b polarization in hadronicZ decays is measured in semileptonic decaysfrom the average energies of the charged leptonand the neutrino. In a data sample of approximately 3 million hadronicZ decays collected by the ALEPHdetector at LEP between 1991 and 1994, 462 ± 31 Λ b candidates are selected using ( Λπ + )- leptoncorrelations. From this event sample, the Λ b polarization is measured to be P Λ b = −0.23 −0.20 +0.24 (stat.) −0.07 +0.08 (syst.).