Measurement of the J/? Polarization with Respect to the Event Plane in Pb-Pb Collisions at the LHC

作者：Acharya, S.; Adamova, D.; Adler, A.; Rinella, G. Aglieri; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; Ahuja, I.; Akindinov, A.; Al-Turany, M.; Aleksandrov, D.; Alessandro, B.; Alfanda, H. M.; Alfaro Molina, R.; Ali, B.; Ali, Y.; Alici, A.; Alizadehvandchali, N.; Alkin, A.; Alme, J.; Alocco, G.; Alt, T.; Altsybeev, I.; Anaam, M. N.; Andrei, C.; Andronic, A.; Anguelov, V.; Antinori, F.; Antonioli, P.; Anuj, C.; Apadula, N.; Aphecetche, L.; Appelshaeuser, H.; Arcelli, S.

来源：Physical Review Letters, 2023, 131(4): 042303.

DOI：10.1103/PhysRevLett.131.042303

• MAGNETIC-FIELD
• HEAVY
• SUPPRESSION
• QUARKONIUM

We study the polarization of inclusive J=. produced in Pb-Pb collisions at ffisffiffiNffiffiNffiffiffip 1/4 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=. 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 3.9s 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.