Thermal Hadron Production by QCD Hawking Radiation

The QCD counterpart of Hawking radiation from black holes leads to thermal hadron production in high energy collisions, from $e^+e^-$ annihilation to heavy ion interactions. This hadronic radiation is formed by tunnelling through the event horizon of colour confinement and is emitted at a universal temperature $T_H \simeq (\sigma /2 \pi)^{1/2}$, where $\sigma$ denotes the string tension. Since the event horizon does not allow information transfer, the radiation is thermal ``at birth''.Comment: 17 pages, 12 figures; updated version of an invited talk at the workshop "Critical Point and Onset of Deconfinement", Firenze/Italy, July 3-6, 200

Parton Percolation in Nuclear Collisions

An essential prerequisite for quark-gluon plasma production in nuclear collisions is cross-talk between the partons from different nucleons in the colliding nuclei. The initial density of partons is determined by the parton distribution functions obtained from deep inelastic lepton-hadron scattering and by the nuclear geometry; it increases with increasing $A$ and/or $\sqrt s$. In the transverse collision plane, this results in clusters of overlapping partons, and at some critical density, the cluster size suddenly reaches the size of the system. The onset of large-scale cross-talk through color connection thus occurs as geometric critical behavior. Percolation theory specifies the details of this transition, which leads to the formation of a condensate of deconfined partons. Given sufficient time, this condensate could eventually thermalize. However, already the onset of parton condensation in the initial state, without subsequent thermalization, leads to a number of interesting observable consequences.Comment: 15 pages, 18 figures; Lectures at the International School of Physics "Enrico Fermi", Varenna/Italy, 6.-16. 8. 200

Charm and Beauty in a Hot Environment

We discuss the spectral analysis of quarkonium states in a hot medium of deconfined quarks and gluons, and we show that such an analysis provides a way to determine the thermal properties of the quark-gluon plasma.Comment: 14 pages, 15 figures; presented at the meeting "A Sense of Beauty in Physics", honoring the 70th birthday of Adriano Di Giacomo; Pisa, Jan. 26 -27, 200

Quarkonium Binding and Entropic Force

A Q-Qbar bound state represents a balance between repulsive kinetic and attractive potential energy. In a hot quark-gluon plasma, the interaction potential experiences medium effects. Color screening modifies the attractive binding force between the quarks, while the increase of entropy with Q-Qbar separation gives rise to a growing repulsion. We study the role of these phenomena for in-medium Q-Qbar binding and dissociation. It is found that the relevant potential for Q-Qbar binding is the free energy F; with increasing Q-Qbar separation, further binding through the internal energy U is compensated by repulsive entropic effects.Comment: 11 pages, 8 figure

A Brief History of J/Psi Suppression

Statistical QCD predicts that strongly interacting matter will become deconfined at high temperatures and/or densities. The aim of high energy nuclear collisions is to study the onset of deconfinement and the properties of deconfined media in the laboratory. Hence it is essential to define an unambiguous and experimentally viable probe for deconfinement. Twelve years ago, T. Matsui and I proposed that \J~production should constitute such a probe \cite{M&S}, and I want to sketch here rather briefly the evolution of this idea in the light of subsequent experimental and theoretical work.Comment: 7 pages, latex, two figures (included

QCD & QGP: A Summary

Contents: 1. The Thermodynamics of Quarks and Gluons 2. Hard Probes: Colour Deconfinement 3. Electromagnetic Probes: Chiral Symmetry Restoration 4. Soft Probes: Equilibration and Expansion 5. ConclusionsComment: 20 pages, Latex; Theory Summary, International Conference on the Physics and Astrophysics of the Quark-Gluon Plasma (ICPA-QGP'97), Jaipur/India, March 15 - 21, 199

Colour deconfinement in hot and dense matter

We first introduce the conceptual basis of critical behaviour in strongly interacting matter, with colour deconfinement as QCD analog of the insulator-conductor transition and chiral symmetry restoration as special case of the associated shift in the mass of the constituents. Next we summarize quark-gluon plasma formation in finite temperature lattice QCD. We consider the underlying symmetries and their spontaneous breaking/restoration in the transition, as well as the resulting changes in thermodynamic behaviour. Finally, we turn to the experimental study of strongly interacting matter by high energy nuclear collisions, using charmonium production to probe the confinement status of the produced primordial medium. Recent results from Pb-Pb collisions at CERN may provide first evidence for colour deconfinement.Comment: 11 pages tex, uses macro-hs.tex, 10 figures; talk given at CRIS '96, First Catania Relativistic Ion Studies, Acicastello, Italy, May 27 - 31, 1996; to appear in the Proceeding

Phase Transitions in QCD

At high temperatures or densities, hadronic matter shows different forms of critical behaviour: colour deconfinement, chiral symmetry restoration, and diquark condensation. I first discuss the conceptual basis of these phenomena and then consider the description of colour deconfinement in terms of symmetry breaking, through colour screening and as percolation transition.Comment: 19 pages, 14 figure