Measurement of the Y(1s), Y (2S), and Y (3S) Polarizations in pp Collisions at s=7TeV
The polarizations of the Υ(1S), Υ(2S), and Υ(3S) mesons are measured in proton-proton collisions at s√=7 TeV, using a data sample of Υ(nS)→μ+μ− decays collected by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters λϑ, λφ, and λϑφ, as well as the frame-invariant quantity λ˜, are presented as a function of the Υ(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges |y|<0.6 and 0.6<|y|<1.2. No evidence of large transverse or longitudinal polarizations is seen in the explored kinematic region.