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 / Acharya, S., Adamová, D., Adler, A., Adolfsson, J., Aglieri Rinella, G., Agnello, M., Agrawal, N., Ahammed, Z., Ahmad, S., Ahn, S.U., Ahuja, I., Akbar, Z., Akindinov, A., Al-Turany, M., Alam, S.N., Aleksandrov, D., Alessandro, B., Alfanda, H.M., Alfaro Molina, R., Ali, B., et al.. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - 815:(2021). [10.1016/j.physletb.2021.136146]
First measurement of quarkonium polarization in nuclear collisions at the LHC
L. CunqueiroMembro 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.| File | Dimensione | Formato | |
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ALICE Collaboration_First measurement_2021.pdf
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