Conde, P.Garrido Beltrán, LluísPeralta, D.HERA-B Collaboration2014-07-282014-07-2820091434-6044https://hdl.handle.net/2445/56366A study of the angular distributions of leptons from decays of J/ψ"s produced in p-C and p-W collisions at s√=41.6~GeV has been performed in the J/ψ Feynman-x region −0.34<x F <0.14 and for J/ψ transverse momenta up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3×105 J/ψ"s reconstructed in both the e + e − and μ + μ − decay channels, indicate that J/ψ"s are produced polarized. The magnitude of the effect is maximal at low p T . For p T >1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises.8 p.application/pdfengcc by (c) HERA-B Collaboration, 2009http://creativecommons.org/licenses/by/3.0/AstronomiaAstrofísicaFísica nuclearPartícules (Física nuclear)Teoria quàntica de campsAstronomyAstrophysicsNuclear physicsParticles (Nuclear physics)Quantum field theoryinfo:eu-repo/semantics/article5776482014-07-28info:eu-repo/semantics/openAccess