The polarization of inclusive J/ψ and Υ (1S) produced in Pb–Pb collisions at √sNN = 5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5 < y < 4 and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters λθ , λ φ and λ θ φ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval 2 < pT < 10 GeV/c and pT < 15 GeV/c for the J/ψ and Υ (1S), respectively. The polarization parameters for the J/ψ are found to be compatible with zero, within a maximum of about two standard deviations at low pT , for both reference frames and over the whole pT range. The values are compared with the corresponding results obtained for pp collisions at √s = 7 and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for Υ (1S) production in Pb–Pb collisions are also consistent with zero.

First measurement of quarkonium polarization in nuclear collisions at the LHC

L. Cunqueiro
Membro del Collaboration Group
;
2021

Abstract

The polarization of inclusive J/ψ and Υ (1S) produced in Pb–Pb collisions at √sNN = 5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5 < y < 4 and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters λθ , λ φ and λ θ φ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval 2 < pT < 10 GeV/c and pT < 15 GeV/c for the J/ψ and Υ (1S), respectively. The polarization parameters for the J/ψ are found to be compatible with zero, within a maximum of about two standard deviations at low pT , for both reference frames and over the whole pT range. The values are compared with the corresponding results obtained for pp collisions at √s = 7 and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for Υ (1S) production in Pb–Pb collisions are also consistent with zero.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1655193
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