Measurement of the prompt J/ψ and ψ(2S) 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. Theprompt J/ψ and ψ(2S) polarization parameters λϑ, λϕ, andλϑϕ, 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 and0.6 < |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.