CERN Accelerating science

In 1986, the modification of quarkonium production was first proposed as a signature of the formation of a Quark Gluon Plasma. While the central role of quarkonium in the understanding of the QGP is indisputable, the direct link between the expected sequential suppression, in a very hot medium, and the experimental observations is not yet completely settled. Several other mechanisms, related to either the formation of a hot medium, such as quarkonium regeneration, or to the presence of cold nuclear matter, are well-known key effects in the interpretation of the results.

This talk reviews very recent LHC Run 2 results obtained with the ALICE detector, which is designed to study quarkonium in two rapidity ranges,  at mid-rapidity ($|y|<0.9$) in the dielectron decay channel and at forward rapidity ($2.5<y<4$) in the dimuon channel, both down to zero transverse momentum. Results on the J/$\psi$ nuclear modification factor ($R_{\rm{AA}}$) and azimuthal anisotropy, measured, with high precision, at the highest LHC Pb-Pb energy ($\sqrt{s_{\rm{NN}}}$= 5.02 TeV), will be presented. Results on the other quarkonium states as the loosely bound $\psi(2S)$ and the heavier bottomonium resonances will also be addressed. The impact of these measurements on our understanding of quarkonium production, absorption and regeneration in the hot QCD matter will be discussed by comparing both to results from lower energies and to theoretical predictions. Finally, results on $J/\psi$ production in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$= 8.16 TeV will also be presented and compared to models including different sources of cold nuclear matter effects.