Measurement of the Prompt $J/\psi$ and $\psi$(2S) Polarizations in $pp$ Collisions at $\sqrt{s}$ = 7 TeV

The CMS collaboration
Phys.Lett.B 727 (2013) 381-402, 2013.

Abstract (data abstract)
CERN-LHC. The polarizations of prompt J/psi and psi(2S) mesons are measured in proton-proton collisions at sqrt(s) = 7 TeV, using a dimuon data sample collected in 2011 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.9 fb^-1. The prompt J/psi and psi(2S) polarization parameters Lambda-Theta, Lambda-Phi, Lambda-Theta-Phi, as well as the frame-invariant Lambda-Tilde, are measured from the dimuon decay angular distributions in three different polarization frames. The J/psi 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 psi(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. The tables below list the results of the angular anisotropy parameters Lambda-Theta, Lambda-Phi, Lambda-Theta-Phi and the frame-invariant parameter Lambda-Tilde, for the J/psi and psi(2S) states in the Collins-Soper (CS), helicity (HX), and perpendicular helicity (PX) frames, along with their total uncertainties (68.3%, 95.5%, and 99.7% CL) and statistical uncertainties only (68.3% CL) for different bins of J/psi or psi(2S) transverse momentum pT and absolute rapidity |y|.

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