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arXiv · 1805.04374

Measurement of the inclusive J/$ψ$ polarization at forward rapidity in pp collisions at $\sqrt{s} = 8$ TeV

ALICE Collaboration
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Abstract

We report on the measurement of the inclusive J/$ψ$ polarization parameters in pp collisions at a center of mass energy $\sqrt{s} = 8$ TeV with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.23 pb$^{-1}$. J/$ψ$ resonances are reconstructed in their di-muon decay channel in the rapidity interval $2.5 < y < 4.0$ and over the transverse-momentum interval $2 < p_{\rm T} < 15$ GeV/$c$. The three polarization parameters ($λ_θ$, $λ_φ$, $λ_{θφ}$) are measured as a function of $p_{\rm T}$ both in the helicity and Collins-Soper reference frames. The measured J/$ψ$ polarization parameters are found to be compatible with zero within uncertainties, contrary to expectations from all available predictions. The results are compared with the measurement in pp collisions at $\sqrt{s} = 7$ TeV.

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ALICE Collaboration. 2019-01-17. Measurement of the inclusive J/$ψ$ polarization at forward rapidity in pp collisions at $\sqrt{s} = 8$ TeV. https://doi.org/10.1140/epjc%2Fs10052-018-6027-2

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