Lambda, abti-Lambda polarization in NOMAD

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The Λ polarization in \nu_\mu charged current interactions has been measured in the NOMAD experiment. The event sample (8087 reconstructed Λ 's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. 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). These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. A significant transverse polarization (in the direction orthogonal to the Λ 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 Λ transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron–hadron experiments. download PDF from Nuclear Physics B server

We present a measurement of the polarization of Image hyperons produced in νμ charged current interactions. The full data sample from the NOMAD experiment has been analyzed using the same V0 identification procedure and analysis method reported in a previous paper [NOMAD Collaboration, Nucl. Phys. B 588 (2000) 3] for the case of Λ hyperons. The Image polarization has been measured for the first time in a neutrino experiment. The polarization vector is found to be compatible with zero. download PDF from Nuclear Physics B server