Speaker
Description
Quarkonium production provides a powerful probe of the deconfinement of strongly interacting matter in high-energy heavy-ion collisions. Because the binding potential of heavy quark--antiquark pairs is screened in the quark--gluon plasma (QGP), measurements of quarkonium yields and polarization can reveal the onset and properties of this deconfined medium. For the J/$\psi$ meson, a bound state of a charm quark and antiquark, (re-)generation during the QGP evolution is established as the dominant production mechanism at low transverse momentum ($p_{\rm T}$) and in central Pb--Pb collisions at LHC energies. This regeneration process serves as a direct probe of charm-quark deconfinement and the degree of thermalization in the QGP.
In this talk, we present comprehensive measurements of the J/$\psi$ nuclear modification factor $R_{\rm AA}$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$~TeV. Furthermore, new results on J/$\psi$ polarization in heavy-ion collisions will be discussed, providing an additional handle on the quarkonium production mechanism and possible modifications of spin alignment in the QGP. All results are compared with state-of-the-art theoretical model calculations to constrain quarkonium production dynamics and to characterize the properties of the deconfined medium.
