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

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 experiment at the LHC, corresponding to an integrated luminosity of 4.9 fb-1. The prompt J/ψ and ψ(2S) polarization parameters λθ{symbol}, λφ, and λθ{symbol}φ, 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<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. © 2013 CERN.