New Year thoughts ( winding up January and February 2015)

                                                       What other effects?

In relativistic heavy ion collisions, quarkonia are probes to study the properties of the deconfined state of partonic matter, the Quark–Gluon Plasma (QGP), predicted by QCD at high temperature and pressure. Since quarkonia are produced at the early stage of the collision, they are expected to interact with the QGP throughout its evolution. Quarkonium states are suppressed in the QGP in the colour-screening scenario, with different dissociation probabilities for the various mass states, depending on their binding energy. 

However, other hot nuclear matter effects besides colour screening, as well as cold nuclear matter (CNM) effects, do complicate this simple picture of suppression. Cold nuclear matter effects can be separated into initial and final-state effects. Cold nuclear matter effects can be studied in proton–nucleus (p–A) collisions, where the QGP is not expected to be formed. Charmonium states have been extensively measured in p–A collisions at various collision energies up to the LHC energies. Bottomonium production has recently been studied with the increased energy and luminosity available in the collider experiments at RHIC and the LHC (also in forward rapidities).