Speaker
Description
The quark-gluon plasma (QGP) is a strongly-interacting deconfined state of matter produced in ultra-relativistic heavy-ion collisions. In order to study the QCD matter phase of its evolution, quarkonia, bound states of a heavy quark and antiquark pair, are preferred tools as they are sensitive to the first stages of the collision and to the evolution of the created system.
Measurements of the azimuthal anisotropies (expressed as elliptic and triangular flows, $v_2$ and $v_3$ respectively) shed a light on collective behaviors of the particles within this hot and dense medium. For the $J/\psi$, the regeneration of charm quarks and geometrical anisotropies typically result in a non-zero $v_2$ while fluctuations in the medium are related to the $v_3$.
Measuring the azimuthal anisotropies of these hard probes gives us information regarding their own production mechanisms, and the formation of the QGP.
In this contribution, I review the results regarding the $J/\psi$ flow, from the first measurements at RHIC in Au-Au collisions at $\sqrt{s_{NN}}=200$ GeV, to the most recent ones provided by the LHC collaborations. Part of the measurements concern Pb-Pb collisions (up to $\sqrt{s_{NN}}=5.02$ TeV) in which the $J/\psi$ exhibits a significant non-zero $v_2$ in a wide centrality and $p_T$ range as well as a significant non-zero $v_3$. Other measurements focus on smaller systems like p-Pb. The p-Pb system, which is typically used as a standard candle for CNM effects in Pb-Pb, does display a non-zero $v_2$ for $3 < p_T < 6$ GeV/c whose magnitude is even comparable to the one from Pb-Pb collisions. The smallest hadronic system p-p is also being investigated. Proof of the $J/\psi$ flow in p-p would make a compelling case for collectivity in small systems.
