The Lambda and Lambda-bar polarizations in muon neutrino charged current
interactions have been measured in the NOMAD experiment. The event sample (8087
reconstructed Lambda's and 649 Lambda-bar's) is more than an order of magnitude
larger than that of previous bubble chamber experiments, while the quality of
event reconstruction is comparable. For the Lambda hyperons we observe negative
polarization along the W-boson direction which is enhanced in the target
fragmentation region: Px(xF < 0) = -0.21 +- 0.04 (stat) +- 0.02 (sys). In the
current fragmentation region we find Px(xF > 0) = -0.09 +- 0.06 (stat) +-
0.03(sys). A significant transverse polarization (in the direction orthogonal
to the Lambda production plane) has been observed for the first time in a
neutrino experiment: Py = -0.22 +- 0.03 (stat) +- 0.01 (sys). The dependence of
the absolute value of Py on the Lambda transverse momentum with respect to the
hadronic jet direction is in qualitative agreement with the results from
unpolarized hadron-hadron experiments. The polarization vector of Lambda-bar
hyperons measured for the first time in neutrino interactions is found to be
consistent with zero.Comment: 5 pages, a contrubution to DIS2002 Conference, Cracow (April, 29 -
May, 4