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Adams, M.; Albrecht, H.; Amorim, A.; Aplin, S. J.; Balagura, V.; Barsukova, O.; Bastos, J.; Batista, J.; Bauer, Th. S.; Belkov, A.; Belotelov, I.; Bertin, A.; Bobchenko, B.; Böcker, M.; Buchholz, P.; Conde, P.; Cruse, C.; Dam, M.; Danilov, M.; Deppe, H.; Ehret, K.; Eisele, F.; Emeliyanov, D.; Fabbri, L.; Feuerstack-Raible, M.; Flammer, J.; Gellrich, A.; Goloubkov, D.; Golutvin, I.; Gouchtchine, O.; Goulart, D. C.; Gradl, S.; Gradl, W.; Guilitsky, Yu; Hernández, J. M.; Hofmann, W.; Hohlmann, M.; Hott, T.; Husemann, U.; Igonkina, O.; Ispiryan, M.; Karabekyan, S.; Karpenko, N.; Keller, S.; Kessler, J.; Knöpfle, K. T.; Kolanoski, H.; Krauss, C.; Kreuzer, P.; Kupper, S.; Lanyov, A.; Lau, K.; Masciocchi, S.; Medin, G.; Mevius, M.; Mizuk, R.; Muresan, R.; zur Nedden, M.; Negodaev, M.; Nowak, S.; Ouchrif, M.; Pernack, R.; Pestotnik, R.; Petersen, B. AA; Pleier, M. A.; Poli, M.; Pose, D.; Pugatch, V.; Riu, I.; Robmann, P.; Rybnikov, V.; Sánchez, F.; Schmidt, B.; Schwanke, U.; Schwartz, A. J.; Schwarz, A. S.; Schwingenheuer, B.; Solunin, S.; Somov, A.; Somov, S.; Spengler, J.; Spighi, R.; Spiridonov, A.; Stegmann, C.; Symalla, M.; Tsakov, I.; Uwer, U.; Villa, M.; Vitale, A.; Vukotic, I.; Walter, M.; Wang, J. J.; Wegener, D.; Werthenbach, U.; Wolters, H.; Zaitsev, Yu; Zeuner, T.; Zhelezov, A.; Živko, T.; Zoccoli, A.
The European physical journal. C, Particles and fields, 04/2009, Letnik: 60, Številka: 4Journal Article
A study of the angular distributions of leptons from decays of J / ψ ’s produced in p-C and p-W collisions at 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 2.3×10 5 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.
