Colour deconfinement in nuclear collisions

Abstract

Abstract:QCD predicts that strongly interacting matter will undergo a transition from a state of hadronic constituents to a plasma of unbound quarks and gluons. We first survey the conceptual features of this transition and its description in finite temperature lattice QCD, before we address its experimental investigation through high energy nucleus-nucleus collisions. After considering the conditions achievable in such collisions, we discuss the possible probes to check if the produced medium in its early stages was indeed deconfined. We then elaborate the method that has emerged and the results which were obtained using the most extensively studied deconfinement probe, the suppression of charmonium production. In closing, we discuss possible supporting information provided through the study of soft hadronic probes.

Ultrarelativistic Nucleus–Nucleus Collisions and the Quark–Gluon Plasma

“…It is consequently of particular relevance to find experimental observables which carry information (preferentially) from one particular stage, in particular about the QGP phase. Specific probes of QGP have been proposed [21,22] and are currently being studied experimentally: i) direct photons [23]; ii) low-mass dileptons [24]; iii) strangeness [25]; v) charmonium suppression [3]; vi) jet-quenching [26]; vii) fluctuations [12,27].…”

“…[76]) assumes that all charm quarks are produced in primary hard collisions and equilibrate 3 in the quark-gluon plasma. An important corollary of this assumption is that no J/ψ mesons are preformed in the QGP, implying that the dissociation of J/ψ in QGP [3] is complete. As noted above, recent lattice QCD calculations show that the J/ψ mesons may not be dissociated in a deconfined medium below about 1.5T c [57].…”

“…No secondary production of charm in the initial and final state was included in our calculations. Final state effects like nuclear absorption of J/ψ [3] are also neglected. First RHIC data on J/ψ production support the current predictions, although the experimental errors are for the moment too large to allow firm conclusions.…”

“…The opposite phase transition, from quarks and gluons to hadronic matter, took place about 10 −5 s after the Big Bang, the primeval event which is at the origin of our Universe. The core of the physics program of ultrarelativistic nucleus-nucleus collisions research [2] is the study of the properties of strongly interacting matter at high energy density, in particular its phase diagram and the properties of quark-gluon plasma (QGP) [3].…”

Novel subjet observables for jet quenching in heavy-ion collisions

“…Interactions of high-energy partons with a strongly coupled hot partonic medium -a quark-gluon plasma (QGP) [1][2][3][4] created in heavy-ion collisions, leading to modifications of the internal jet structure (jet quenching), was first proposed in [5] and is studied as a sensitive probe of the medium properties [6][7][8]. Experiments at RHIC and the LHC observed a strong suppression of high transverse momentum particle yields [9][10][11][12][13][14][15], suppression of inclusive and semi-inclusive yields of fully reconstructed jets [16][17][18][19][20], and, more recently, the internal structure of the jets [21][22][23][24][25] for detailed studies of jet quenching.…”