Quarkonium in the Quark-Gluon Plasma: An Experimental Overview

                                                                             EMMI FEATURED TALK

For almost forty years, quarkonium, the bound state of charm-anticharm or bottom-antibottom quarks, is considered a unique probe to investigate the properties of the quark-gluon plasma (QGP).
This state of matter, composed by deconfined quarks and gluons, was present in the early instants of the universe and is produced experimentally in ultrarelativistic heavy-ion collisions.
In the QGP the binding between the quark and antiquark pair is expected to be screened, due to the very hot and dense environment, leading to a suppression in the production of quarkonia.
Since quarkonia come in a rich variety of states, differently bound and hence differently affected by the QGP, their melting is expected to be directly connected to the temperature reached in the nucleus-nucleus collisions.
This suppression picture is, however, complicated by several other hot or cold matter effects which might influence the quarkonium yields. The large number of quarks and antiquarks in the plasma may, for example, give rise to another mechanism, called recombination, which favors the production of new quarkonia, balancing the suppression to a certain extend. Furthermore, mechanisms related to the underlying presence of cold nuclear matter effects (such as nuclear shadowing, energy loss or nuclear absorption), investigated in proton-nucleus interactions, are also influencing the quarkonium yields. 
The interplay between all these mechanisms depends on the quarkonium state and on the explored collision energy. Therefore, the possibility to study different charmonium and bottomonium states over a very broad collision range, from SPS up to RHIC and LHC energies, put quarkonium in an ideal position to access the properties of the QGP created in the nucleus-nucleus interactions.
 

In this talk, an experimental overview of quarkonium results obtained so far in heavy-ion collisions will be presented and prospects for future measurements in the next years will also be discussed.

EMMI Physics Days 2024