文档介绍：Physics Letters B 727 (2013) 381–402 Contents lists available at ScienceDirect Physics Letters B ate/physletb Measurement of the prompt J /ψ and ψ( 2S ) polarizations in pp collisions at √ s = 7TeV ?.CMS Collaboration ? CERN, Switzerland article info abstract Article history: Received 23 July 2013 Received in revised form 24 October 2013 Accepted 25 October 2013 Available online 29 October 2013 Editor: M. Doser Keywords: CMS Physics Quarkonium production Quarkonium polarization 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 experiment at the LHC, corresponding to an integrated luminosity of fb ? J /ψ and ψ( 2S )polarization parameters λ?, λ?,and λ??, as well as the frame-invariant quantity ?λ, are measured from the dimuon decay angular distributions in three different polarization frames. The J /ψ results are obtained in the transverse momentum range 14 < p T < 70 GeV, in the rapidity intervals | y | < 0 .6and0 . 6 < | y | < 1 .2. The corresponding ψ( 2S ) results cover 14 < p T < 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. ? 2013 CERN. Published by Elsevier . All rights reserved. 1. Introduction After considerable experimental and theoretical efforts over the past decades, the understanding of quarkonium production in hadron collisions is still not fully settled [1] . In particular, the polarization of J /ψ mesons is not satisfactorily described in the context of nonrelativistic quantum chromodynamics (NRQCD) [2] , where the purely perturbative color-singlet production [3] - plemented by processes including possible nonperturbative tran- sitions from colored quark pairs to the observable bound states. The S-wave quarkonia directly produced at high transverse mo- mentum, p T, are predicted to be tr