Helmut Satz

J/psi suppression by quark-gluon plasma formation

If high energy heavy ion collisions lead to the formation of a hot quark-gluon plasma, then colour screening prevents ce binding in the deconfined interior of the interaction region. To study this effect, the temperature dependence of the screening radius, as obtained from lattice QCD, is compared with the J/q/radius calculated in charmonium models. The feasibility to detect this effect clearly in the dilepton mass spectrum is examined. It is concluded that J/~, suppression in nuclear collisions should provide an unambiguous signature ofquark-gluon plasma formation. Statistical QCD predicts that strongly interacting matter should at sufficiently high density undergo a transition from hadronic matter to quark-gluon plasma ~ . It is hoped that energetic nuclear collisions will allow us to study this transition in the laboratory :2. The experimental detection of plasma formation thus becomes crucial: what observable signatures does the predicted new form of matter provide? Signatures proposed so far include ~3 real or virtual photons, the Pa- distribution of secondary hadrons, and the relative production rate of strange particles. Non-thermal processes as well as uncertainties in the plasma evolution do, however, lead to considerable ambiguity for the signals considered up to now. We want to present here another type of signature for plasma formation, which directly reflects deconfinement and appears to provide a rather clear and model-independent test.

Heavy quarkonium physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

Color screening and deconfinement for bound states of heavy quarks

We study the binding and deconfinement of heavy quarks in a thermal environment, using a non-relativistic confinement potential model with color screening. As a result, we obtain the dependence of the dissociation energies, the binding radii and the masses of heavy quark resonances (charmonium and bottonium states) on the color screening lengthrD of the medium, and we determine for the different resonances those values ofrD below which no more binding is possible. Finally, we consider the implication of our results on resonance suppression as signal for deconfinement.

Quarkonium interactions in hadronic matter

Abstract The cross section for the J /ψ and ϒ interaction with light hadrons is calculated in short-distance QCD, based on the large heavy quark mass and the resulting large energy gap to open charm or beauty. The low energy form of the cross section is determined by the gluon structure functions at large x ; hence it remains very small until quite high energies. This behaviour is experimentally confirmed by charm phoroproduction data. It is shown to exclude J /ψ absorption in confined hadronic matter of the size or density attainable in nuclear collisions; in contrast, the harder gluon spectrum in deconfined matter allows break-up interactions.

A quantitative analysis of charmonium suppression in nuclear collisions

Data from J/ψ and ψ′ production in p - A collisions are used to determine the cross section for absorption of pre-resonance charmonium in nuclear matter. The J/ψ suppression in O - Cu, O - U and S - U collisions is fully reproduced by the corresponding nuclear absorption, while Pb - Pb collisions show an additional suppression increasing with centrality. We study the onset of this change in terms of hadronic comover interactions and conclude that so far no conventional hadronic description can consistently account for all data. Deconfinement, starting at a critical point determined by central S - U collisions, is in accord with the observed suppression pattern.

Charmonium properties in hot quenched lattice QCD

We study the properties of charmonium states at finite temperature inquenched QCD on large and fine isotropic lattices. We perform a detailedanalysis of charmonium correlation and spectral functions both below and above

Charmonium composition and nuclear suppression

T_c

The spectral analysis of strongly interacting matter

. Our analysis suggests that both S wave states (

Intermittency and critical behaviour

J/psi

THE CRITICAL EXPONENTS OF THE DECONFINEMENT TRANSITION IN SU(2) LATTICE GAUGE THEORY

and