Measurement of the Lambda(b) polarization in Z decays

The Lambda(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 Lambda(b) candidates are selected using ( Lambdapi(+))- leptoncorrelations. From this event sample, the Lambda(b) polarization is measured to be P- Lambdab = -0.23(-0.20)(+0.24)(stat.)(-0.07)(+0.08)(syst.).