Measurement of the inclusive J/$\psi$ polarization at forward rapidity in pp collisions at $\sqrt{s} = 8$ TeV
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Abstract (data abstract)
CERN-LHC. Measurement of the inclusive J/psi polarization at forward rapidity in pp collisions at sqrt{s} = 8 TeV. Inclusive J/psi polarization parameters is studied in proton-proton collisions at a centre-of-mass energy sqrt{s} = 8 TeV, using the ALICE detector at the CERN LHC. The J/psi mesons are reconstructed, via their decay to a muon pair, in the rapidity interval 2.5 < y < 4.0. The polarization parameters (lambda_theta, lambda_phi and lambda_thetaphi) of inclusive J/psi, as well as an invariant frame quantity, are studied in both helicity and Collins-Soper frames as a function of transverse momentum (p_T) in the interval 2 < p_T < 15 GeV/c. The p_T integrated results are projected in 2-D parameter-space. The measurements exhibit no polarization of inclusive J/psi within experimental uncertainties. In the paper, results are compared to previous measurements at sqrt{s} = 7 TeV from ALICE and LHCb, and also to up-to-date NLO predictions of the Color-Singlet-Model and the NRQCD calculation at sqrt{s} = 8 TeV.