arXiv subjects
Publications and source records attributed to H. Satz.
The study of high energy nuclear collisions has entered a new stage with RHIC; it therefore seems a good time to ask what we have learned from the experimental results obtained up to now. I recall what we had expected to find when the SPS and AGS programs were started, summarize what actually was found, and then try to assess what we have learned from the results.
The geometric clustering of partons in the transverse plane of nuclear collisions leads for increasing A or sqrt(s) to percolation. In the resulting condensate, the partons are deconfined but not yet in thermal equilibrium. We discuss quarkonium dissociation in this precursor of the quark-gluon plasma, with an onset of dissociation when the saturation scale of the parton condensate reaches that of the given quarkonium state.
I discuss the phase structure of strongly interacting matter at high temperatures and densities, as predicted by statistical QCD, and consider in particular the nature of the transition of hot hadronic matter to a plasma of deconfined quarks and gluons.
The aim of high energy nuclear collisions is to study the transition from hadronic matter to a plasma of deconfined quarks and gluons. I review the basic questions of this search and summarize recent theoretical developments in the field.
We use recent lattice data on the heavy quark potential in order to determine the dissociation temperatures of different quarkonium states in hot strongly interacting matter. Our analysis shows in particular that certain quarkonium states dissociate below the deconfinement point.
Continuous phase transitions in spin systems can be formulated as percolation of suitably defined clusters. We review this equivalence and then discuss how in a similar way, the color deconfinement transition in SU(2) gauge theory can be treated as a percolation phenomenon. In the presence of an external field, spin systems cease to show thermal critical behavior, but the geometric percolation transition persists (Kertész line). For $H\not=0$, we study the relation between percolation and pseudocritical behavior, both for continuous and first order transitions, and show that it leads to the necessity of an $H$-dependent cluster definition. A viable formulation of this kind could serve as definition of deconfinement in QCD with dynamical quarks.
The q-state Potts model can be formulated in geometric terms, with Fortuin-Kasteleyn (FK) clusters as fundamental objects. If the phase transition of the model is second order, it can be equivalently described as a percolation transition of FK clusters. In this work, we study the percolation structure when the model undergoes a first order phase transition. In particular, we investigate numerically the percolation behaviour along the line of first order phase transitions of the 3d 3-state Potts model in an external field and find that the percolation strength exhibits a discontinuity along the entire line. The endpoint is also a percolation point for the FK clusters, but the corresponding critical exponents are neither in the Ising nor in the random percolation universality class.
About 40-50 % of the quarkonium ground states J/psi(1S) and Upsilon(1S) produced in hadronic collisions originate from the decay of higher excitations. In a hot medium, these higher states are dissociated at lower temperatures than the more tightly bound ground states, leading to a sequential suppression pattern. Using new finite temperature lattice results, we specify the in-medium potential between heavy quarks and determine the dissociation points of different quarkonium states. On the basis of recent CDF data on bottomonium production, we then obtain first predictions for sequential Upsilon suppression in nuclear collisions.
Recent lattice studies of string breaking in QCD with dynamical quarks determine the in-medium temperature dependence of the heavy quark potential. Comparing this to the binding energies of different quarkonium states, we check if these can decay into open charm/beauty in a confined hadronic medium. Our studies indicate in particular that the chi_c and the psi dissociate into open charm below the deconfinement point.
For the Ising model, the spin magnetization transition is equivalent to the percolation transition of Fortuin-Kasteleyn clusters; this result remains valid also for the conventional continuous spin Ising model. The investigation of more general continuous spin models may help to obtain a percolation formulation for the critical behaviour in SU(2) gauge theory. We therefore study a broad class of theories, introducing spin distribution functions, longer range interactions and self-interaction terms. The thermal behaviour of each model turns out to be in the Ising universality class. The corresponding percolation formulations are then obtained by extending the Fortuin-Kasteleyn cluster definition; in several cases they illustrate recent rigorous results.
Effective theories are helpful tools to gain an intuitive insight into phenomena governed by complex laws. In this work we show by means of Monte Carlo simulations that Z(2) spin models with only spin-spin interactions approximate rather well the critical behavior of SU(2) gauge theory at finite temperature. These models are then used to formulate an effective description of Polyakov loop percolation, which is shown to reproduce the thermal critical behaviour of SU(2) gauge theory.
We propose that in QCD with dynamical quarks, colour deconfinement occurs when an external field induced by the chiral condensate strongly aligns the Polyakov loop. This effect sets in at the chiral symmetry restoration temperature $T_χ$ and thus makes deconfinement and chiral symmetry restoration coincide. The predicted singular behavior of Polyakov loop susceptibilities at $T_χ$ is shown to be supported by finite temperature lattice calculations.
The paramagnetic-ferromagnetic transition in the Ising model can be described as percolation of suitably defined clusters. We have tried to extend such picture to the confinement-deconfinement transition of SU(2) pure gauge theory, which is in the same universality class of the Ising model. The cluster definition is derived by approximating SU(2) by means of Ising-like effective theories. The geometrical transition of such clusters turns out to describe successfully the thermal counterpart for two different lattice regularizations of (3+1)-d SU(2).
The spontaneous symmetry breaking in the Ising model can be equivalently described in terms of percolation of Wolff clusters. In O(n) spin models similar clusters can be built in a general way, and they are currently used to update these systems in Monte Carlo simulations. We show that for 3-dimensional O(2), O(3) and O(4) such clusters are indeed the physical `islands' of the systems, i.e., they percolate at the physical threshold and the percolation exponents are in the universality class of the corresponding model. For O(2) and O(3) the result is proven analytically, for O(4) we derived it by numerical simulations.
Over the past 15 years, an extensive program of high energy nuclear collisions at BNL and CERN has been devoted to the experimental search for the quark-gluon plasma predicted by QCD. The start of RHIC this year will increase the highest available collision energy by a factor 10. This seems a good time for a critical assessment: what have we learned so far and what can we hope to learn in the coming years?
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.
We propose that in QCD with dynamical quarks, colour deconfinement occurs when an external field induced by the chiral condensate strongly aligns the Polyakov loop. This effect sets in at the chiral symmetry restoration temperature T-chi and thus makes deconfinement and chiral symmetry restoration coincide. The predicted singular behaviour of Polyakov loop susceptibilities at T-chi is shown to be supported by finite temperature lattice calculations.
Using J/psi and open charm photoproduction data, we apply the vector meson dominance model to obtain constraints on the energy dependence of the inelastic J/psi-nucleon cross section. Predictions of short distance QCD are in accord with these constraints, while recently proposed hadronic models for J/psi dissociation strongly violate them.