Measurement of the J /ψ Polarization with Respect to the Event Plane in Pb-Pb Collisions at the LHC
Abstract
We study the polarization of inclusive J /ψ produced in Pb-Pb collisions at √{sNN }=5.02 TeV at the LHC in the dimuon channel, via the measurement of the angular distribution of its decay products. We perform the study in the rapidity region 2.5 <y <4 , for three transverse momentum intervals (2 <pT<4 , 4 <pT<6 , 6 <pT<10 GeV /c ) and as a function of the centrality of the collision for 2 <pT<6 GeV /c . For the first time, the polarization is measured with respect to the event plane of the collision, by considering the angle between the positive-charge decay muon in the J /ψ rest frame and the axis perpendicular to the event-plane vector in the laboratory system. A small transverse polarization is measured, with a significance reaching 3.9 σ at low pT and for intermediate centrality values. The polarization could be connected with the behavior of the quark-gluon plasma, formed in Pb-Pb collisions, as a rotating fluid with large vorticity, as well as with the existence of a strong magnetic field in the early stage of its formation.
- Publication:
-
Physical Review Letters
- Pub Date:
- July 2023
- DOI:
- 10.1103/PhysRevLett.131.042303
- arXiv:
- arXiv:2204.10171
- Bibcode:
- 2023PhRvL.131d2303A
- Keywords:
-
- Nuclear Experiment;
- High Energy Physics - Experiment
- E-Print:
- 17 pages, 2 captioned figures, 1 table, authors from page 12, published version, figures at http://alice-publications.web.cern.ch/node/7845