Measurement of the prompt J/ψ and ψ(2S) polarizations in pp collisions at √s = 7 TeV

Chatrchyan, S. and Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Dragicevic, M. and Erö, J. and Fabjan, C. and Friedl, M. and Frühwirth, R. and Ghete, V. M. and Hörmann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knünz, V. and Krammer, M. and Krätschmer, I. and Liko, D. and Mikulec, I. and Rabady, D. and Rahbaran, B. and Rohringer, C. and Rohringer, H. and Schöfbeck, R. and Strauss, J. and Taurok, A. and Treberer-Treberspurg, W. and Waltenberger, W. and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Molnár, József and Karancsi, János and Ujvári, Balázs and Krajczár, Krisztián and Veres, Gábor (2013) Measurement of the prompt J/ψ and ψ(2S) polarizations in pp collisions at √s = 7 TeV. PHYSICS LETTERS B, 727 (4-5). pp. 381-402. ISSN 0370-2693

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Abstract

The polarizations of prompt J/ψ and ψ(2S) mesons are measured in proton-proton collisions at √s = 7 TeV, using a dimuon data sample collected by the CMS experi- ment at the LHC, corresponding to an integrated luminosity of 4.9 fb−1. The prompt J/ψ and ψ(2S) polarization parameters λϑ, λϕ, and λϑϕ, as well as the frame-invariant quantity ˜λ, are measured from the dimuon decay angular distributions in three dif- ferent polarization frames. The J/ψ results are obtained in the transverse momentum range 14 < pT < 70 GeV, in the rapidity intervals |y| < 0.6 and 0.6 < |y| < 1.2. The corresponding ψ(2S) results cover 14 < pT < 50 GeV and include a third rapidity bin, 1.2 < |y| < 1.5. No evidence of large polarizations is seen in these kinematic regions, which extend much beyond those previously explored.

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