Author/Authors :
NOMAD Collaboration، نويسنده , , P. Astier، نويسنده , , D. Autiero، نويسنده , , A. Baldisseri، نويسنده , , M. Baldo-Ceolin، نويسنده , , M. Banner، نويسنده , , G. Bassompierre، نويسنده , , K. Benslama، نويسنده , , N. Besson، نويسنده , , I. Bird، نويسنده , , B. Blumenfeld، نويسنده , , F. Bobisut، نويسنده , , P. Olivier and J. Bouchez ، نويسنده , , S. Boyd، نويسنده , , A. Bueno، نويسنده , , S. Bunyatov، نويسنده , , L. Camilleri، نويسنده , , A. Cardini، نويسنده , , P.W. Cattaneo، نويسنده , , V. Cavasinni، نويسنده , , et al.، نويسنده ,
Abstract :
The Λ polarization in νμ charged current interactions has been measured in the NOMAD experiment. The event sample (8087 reconstructed Λ ʹs) 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.
