Journal Article

Angular distributions of leptons from J/ψ’s produced in 920 GeV fixed-target proton-nucleus collisions

Bräuer, M., Prystupa, S., Riu, I., Živko, T., Mankel, R., Robmann, P., Vitale, A., Nowak, S., Fabbri, L., Balagura, V., Schwanke, U., Cruse, C., Schmelling, M., Faccioli, P., Groth-Jensen, J., Zimmermann, R., Gorbounov, I., Kessler, J., Buran, T., Kreuzer, P., Bauer, Th. S., Grimaldi, F., Schwingenheuer, B., Padilla, C., Pugatch, V., Spighi, R., Sciacca, F., Lanyov, A., Silva, L., Gradl, S., Emeliyanov, D., Stegmann, C., Wurth, R., Gorišek, A., Pyrlik, J., van Eldik, C., Werthenbach, U., Buchholz, P., Popov, V., Zoccoli, A., Sbrizzi, A., Michetti, A., Adams, M., Karabekyan, S., Abt, I., Masciocchi, S., Sözüer, L., Bruinsma, M., Križan, P., Karpenko, N., Igonkina, O., Goloubkov, D., Belotelov, I., Egorytchev, V., Hohlmann, M., Walter, M., zur Nedden, M., Piccinini, M., Vassiliev, Yu, Wahlberg, H., Jiang, C., Keller, S., Matchikhilian, I., Semprini-Cesari, N., Bertin, A., Khasanov, F., Golutvin, A., Wegener, D., Kisel, I., Albrecht, H., Hott, T., Stanovnik, A., Spengler, J., Walenta, A. H., Kiryushin, Yu, Mizuk, R., Aushev, V., Petersen, B. AA, Hernández, J. M., Bruschi, M., Gradl, W., Dreis, H. B., Subramania, H. S., Hansen, J. D., Böcker, M., Schwennin

2009

Overview

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.

• Publisher: Springer-Verlag,Springer Nature B.V
• Subject: Anisotropy / Astronomy / Astrophysics and Cosmology / Collisions / Dependence / Elementary Particles / Hadrons / Heavy Ions / Helicity / Leptons / Measurement Science and Instrumentation / Nuclear Energy / Nuclear Physics / Physics / Physics and Astronomy / Protons / Quantum Field Theories / Quantum Field Theory / Regular Article - Experimental Physics / String Theory