Search

In proton-nucleus and nucleus-nucleus collisions up to central $S-U$ interactions, the $P_T$-dependence of $J/\psi$ production is determined by initial state parton scattering and pre-resonance nuclear absorption (``normal" $J/\psi$ suppression). The ``anomalous" $J/\psi$ suppression in $Pb-Pb$ collisions must reduce the normal $P_T$ broadening, since it occurs mainly in the central part of the interaction region, where also initial state parton scattering and nuclear absorption are strongest. We thus expect for $< P_T^2 >$ in $Pb-Pb$ collisions a turn-over and decrease with increasing $E_T$., Comment: 6 pages tex-file, 1 PS-Table, 3 PS-Figures

We extend a recent sum rule calculation for inelastic quarkonium-hadron interactions to realistic parton distribution functions; we also include finite target-mass corrections. Both modifications are shown to have no significant effect on the resulting cross section behaviour but the performed analysis gives useful insights on the sum-rule approach in general., Comment: 6-page text in LaTeX plus postscript figure

Data from J/psi and psi' production in p-A collisions are used to determine the cross section for absorption of pre-resonance charmonium in nuclear matter. The J/psi 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., Comment: 37 pages, 12 figures, uses epsfig style, LaTeX

We summarize the theoretical description of charmonium and bottonium production in hadronic collisions and compare it to the available data from hadron-nucleon interactions. With the parameters of the theory established by these data, we obtain predictions for quarkonium production at RHIC and LHC energies., Comment: 11 pages (Plain Tex), 16 figures available on request by fax (41-22) 782 3914

Direct probes for the QGP must be hard enough to resolve sub-hadronic scales ($\ll \la^{-1}$) and distinguish confined and deconfined media. This can be achieved by fast colour charges (jets) and heavy quark resonances (quarkonia). After a general survey, we study quarkonia as confinement probe and show in particular that confined matter is transparent, deconfined matter opaque to \J's., Comment: 13 pages, plain TeX, figures available upon request from the author

We survey how quarkonia can be used to probe colour deconfinement in relativistic nuclear collisions., Comment: plain TeX, 42 pages + 22 figures (not included); hard copies available upon request. Review article to appear in "Quark Gluon Plasma ||", R.C. Hwa (Editor), World Scientific, Singapore

We study charmonium production in hadron-nucleus collisions through the intermediate next-to-leading Fock space component $|(\bar{c}c)_8 g>$, formed by a colour octet $\bar{c}c$ pair and a gluon. We estimate the size of this state and show that its interaction with nucleons accounts for the observed charmonium suppression in nuclear interactions., Comment: Plain TeX, 8 pages, 5 figures available upon request

We analyse the kinematic regimes attainable for $J/\Psi$ and $\Psi'$ production in $p-A$ collisions. With this information, we specify the requirements for an experiment to study the interaction of physical charmonium states in nuclear matter, making use of a heavy ion beam incident on a hydrogen or deuterium target., Comment: plain TeX, 12 pages, 6 Figures available upon request

We calculate the dissociation rates of quarkonium ground states by tunnelling and direct thermal activation to the continuum. For hadronic matter at temperatures $T \leq 0.2$ GeV, neither of these mechanisms leads to a sufficiently large dissociation to explain the experimentally observed suppression of charmonium. Dissociation by sequential excitation to excited energy levels, although OZI-forbidden, requires further analysis., Comment: 8 pages, plain TeX, 2 figures available upon request

Short-distance QCD is employed to calculate the $J/\psi$ survival probability in an equilibrating parton gas, whose evolution is governed by a set of master rate equations. Partons in the early stage of high-energy nuclear collisions may initially not be in equilibrium, but their average transverse momentum is sufficiently high to break up a $Q\bar{Q}$ bound state. Such a break-up during the evolution of the parton gas is shown to cause a substantial $J/\psi$ suppression at both RHIC and LHC energies, using realistic estimates of the initial parton densities. The transverse momentum dependence of the suppression is also shown to be sensitive to the initial conditions and the evolution history of the parton plasma., Comment: 13 pages in RevTex, 5 uuencoded postscript figures included

The cross section for the \J~and \U~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 photoproduction data. It is shown to exclude \J~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., Comment: 10 pages + 4 Figures, plain TeX, CERN-TH.7274/94, BI-TP 94/24 (Minor modifications were made and misprints were removed in this revised version; the figures are available upon request from the authors)

We show that in a hot hadron gas, chiral symmetry restoration and deconfinement lead to a strong suppression of dilepton production by pion annihilation in the continuum above the $\rho-\omega-\phi$ peak. The suppression due to deconfinement persists also for annihilation reactions involving heavier mesons., Comment: plain TeX, 7 pages, CERN-TH.7399/94, BI-TP 94/39 (the needed macro is added to this revised file)

Particle production in central S-A collisions at 200 GeV/A energy is analysed within a thermal model. Present data imply that the strange particles freeze out at a higher temperature than the non-strange particles and that the strangeness saturation is incomplete., Comment: 3 Pages Latex and 3 figures available as Postscript files, talk presented at the EPS Conference 1993, Marseilles, France