arXiv subjects
Publications and source records attributed to H. Satz.
We show that deconfinement in SU(2) gauge theory can be described by the percolation of site-bond clusters of like-sign Polyakov loops. In particular, we find that in 2+1 dimensions the percolation variables coincide with those of the 2-dimensional Ising model.
We first consider the origin of colour deconfinement, comparing in particular spontaneous symmetry breaking and percolation. Next we specify the onset of deconfinement in nuclear collisions through parton percolation, and with parameters determined at SPS energy, we give quantitative predictions for charmonium suppression at RHIC. Finally we show that the parton cascade model leads to similar predictions, starting from a microscopic description of the space-time evolution of the collision.
Using short distance QCD methods based on the operator product expansion, we calculate the $J/ψ$ photoproduction cross section in terms of the gluon distribution function of the nucleon. Comparing the result with data, we show that experimental behaviour of the cross section correctly reflects the $x$-dependence of the gluon distribution obtained from deep inelastic scattering.
We study the clustering of colour strings in the transverse plane of nucleus-nucleus collisions and argue that deconfinement sets in when the string density within a cluster reaches a critical value. We show that this implies a minimal cluster size at the onset of deconfinement, which in turn results in discontinuous behaviour for J/Psi suppression.
According to recent experimental data and theoretical developments we discuss three distinct topics related to strangeness enhancement in nuclear reactions. We investigate the compatibility of multi-strange particle ratios measured in a restricted phase space with thermal model parameters extracted recently in 4pi. We study the canonical suppression as a possible reason for the observed strangeness enhancement and argue that a connection between QGP formation and the undersaturation of strangeness is not excluded.
We compare the predictions of different models for transverse momentum spectra in relativistic heavy ion collisions. Particular emphasis is given to hydrodynamic flow with different assumptions for the radial expansion, and to models based on a superposition of fireballs along the transverse direction (random walk). It is shown that present experimental data cannot distinguish between the models under consideration.
We study the characteristic features of J/Psi suppression by deconfinement. A first order phase transition leads to an essentially discontinuous onset of anomalous J/Psi suppression. The different energy densities required for the dissociation of different charmonium states result in a two-step suppression pattern, in which first the J/Psi's from chi decays are suppressed and subsequently the directly produced J/Psi states. Combining both features leads to a unique form of J/Psi suppression in a deconfining medium.
In proton-nucleus and nucleus-nucleus collisions up to central $S-U$ interactions, the $P_T$-dependence of $J/ψ$ production is determined by initial state parton scattering and pre-resonance nuclear absorption (``normal" $J/ψ$ suppression). The ``anomalous" $J/ψ$ 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 $E_T$.
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.
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.
The most abundantly produced hadron species in $Si\!-\!Au$ collisions at the BNL-AGS (nucleons, pions, kaons, antikaons and hyperons) are shown to be in accord with emission from a thermal resonance gas source of temperature $T\simeq 110$ MeV and baryochemical potential $μ_B \simeq 540$ MeV, corresponding to about 1/3 standard nuclear density. Our analysis takes the isopin asymmetry of the initial state fully into account.
Short-distance QCD is employed to calculate the $J/ψ$ 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 $J/ψ$ 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.
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.
We survey how quarkonia can be used to probe colour deconfinement in relativistic nuclear collisions.
We analyse the kinematic regimes attainable for $J/Ψ$ and $Ψ'$ 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.
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.
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.
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.