Charmonium states in quark-gluon plasma

We discuss how the spectral changes of quarkonia at T _c can reflect the ‘critical’ behaviour of QCD phase transition. Starting from the temperature dependencies of the energy density and pressure from lattice QCD calculation, we extract the temperature dependencies of the scalar and spin-2 gluon condensates near T _c. We also parametrize these changes into the electric and magnetic condensate near T _c. While the magnetic condensate hardly changes across T _c, we find that the electric condensate increases abruptly above T _c. Similar abrupt change is also seen in the scalar condensate. Using the QCD second-order Stark effect and QCD sum rules, we show that these sudden changes induce equally abrupt changes in the mass and width of J/ψ, both of which are larger than 100 MeV at slightly above T _c.      

Physics of strongly coupled quark-gluon plasma

This review covers our current understanding of strongly coupled Quark-Gluon Plasma (sQGP), especially theoretical progress in: (i) explaining the RHIC data by hydrodynamics; (ii) describing lattice data using electric-magnetic duality; (iii) understanding of gauge-string duality known as AdS/CFT and its application for “conformal” plasma. In view of the interdisciplinary nature of the subject, we include a brief introduction into several topics “for pedestrians”. Some fundamental questions addressed are: Why is sQGP such a good liquid? What is the nature of (de)confinement and what do we know about “magnetic” objects creating it? Do they play any important role in sQGP physics? Can we understand the AdS/CFT predictions, from the gauge theory side? Can they be tested experimentally? Can AdS/CFT duality help us understand rapid equilibration/entropy production? Can we work out a complete dynamical “gravity dual” to heavy ion collisions?     

Quantum simulations of strongly coupled quark-gluon plasma

A strongly coupled quark-gluon plasma (QGP) of heavy constituent quasiparticles is studied by a path-integral Monte-Carlo method. This approach is a quantum generalization of the model developed by B.A. Gelman, E.V. Shuryak, and I. Zahed. It is shown that this method is able to reproduce the QCD lattice equation of state and also yields valuable insight into the internal structure of the QGP. The results indicate that the QGP reveals liquid-like rather than gas-like properties. At temperatures just above the critical one it was found that bound quark-antiquark states still survive. These states are bound by effective string-like forces and turn out to be colorless. At the temperature as large as twice the critical one no bound states are observed. Quantum effects turned out to be of prime importance in these simulations.     

Lambdac enhancement from strongly coupled quark-gluon plasma

We propose the enhancement of Lambdac as a novel quark-gluon plasma signal in heavy ion collisions at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider. Assuming a stable bound diquark state in the strongly coupled quark-gluon plasma near the critical temperature, we argue that the direct two-body collision between a c quark and a [ud] diquark would lead to an enhanced Lambdac production in comparison with the normal three-body collision among independent c, u, and d quarks. In the coalescence model, we find that the Lambdac/D yield ratio is enhanced substantially due to the diquark correlation.     

Quantum simulations of strongly coupled quark-gluon plasma

A strongly coupled quark-gluon plasma (QGP) of heavy constituent quasi-particles is studied by a path-integral Monte-Carlo method. This approach is a quantum generalization of the classical molecular dynamics by Gelman, Shuryak, and Zahed. It is shown that this method is able to reproduce the QCD lattice equation of state. The results indicate that the QGP reveals liquid-like rather than gaslike properties. Quantum effects turned out to be of prime importance in these simulations.     

Quantum simulations of strongly coupled quark-gluon plasma

A strongly coupled quark-gluon plasma (QGP) of heavy constituent quasiparticles is studied by a path-integral Monte-Carlo method, which improves the corresponding classical simulations by extending them to the quantum regime. It is shown that this method is able to reproduce the lattice equation of state and also yields valuable insight into the internal structure of the QGP. The results indicate that the QGP reveals liquid-like rather than gas-like properties. At temperatures just above the critical one it was found that bound quark-antiquark states still survive. These states are bound by effective stringlike forces. Quantum effects turned out to be of prime importance in these simulations.     

How should we probe a strongly coupled quark-gluon plasma?

Dramatic changes had occurred with our understanding of quark-gluon plasma, which is now believed to be rather strongly coupled. One set of questions is what is its internal structure: at the moment the best answer seem to be a liquid made of binary bound states. Another set of questions is how to probe it, especially using hard probes of the main interest to this meeting. Three suggestions to be discussed are (i) the ionization losses related to new bound states; (ii) the “conical flow” from quenched jets; (iii) possible new peaks in the dilepton spectra, corresponding to vector mesons above T_c.Arrival of the final proofs: 15 March 2005PACS: 12.38.Mh, 25.75.-q     

Charm production in a quark-gluon plasma

A calculation is made for charm quark production in a longitudinally expanding quark-gluon plasma. A comparison is made with hadronic charm production in ultra-relativistic nuclear collisions assuming an extrapolation from p-p collisions and no plasma formation. The charm yield from a QGP begins to dominate purely hadronic production for plasma temperatures above 315–440 MeV, depending on the bombarding energy of the colliding nuclei and the value assumed for the charm quark mass. Implications for plasma signals, most notably dilepton emission and J/ψ suppression, are discussed.     

Three-particle interactions in a quark-gluon plasma

We explore the influence of three-particle interactions, in either the initial or final state, on the collision rate in a high temperature plasma, and on the rate of quark and anti-quark pair (flavor) production. When the interactions are taken to be screened at the Debye wave numberq dT, three-particle interactions contribute significantly to the collision rate, but only marginally enhance flavor production over that from two-particle interactions. The magnitudes of the rates are, however, sensitive to the infra-red thresholds, which emphasizes the need for a reliable analysis of this issue. Our results also highlight the importance of treating many-particle processes adequately in the space-time evolution of quarks and gluons produced in ultrarelativistic heavy-ion collisions.We thank members of the Theoretical Physics Institute and the School of Physics and Astronomy at the University of Minnesota for their kind hospitality. Special thanks are due to J.I. Kapusta for stimulating discussions. The stay of P. L. at the University of Minnesota was supported by the U.S. Department of Energy under grant No. DOE/DE-FG02-87ER-40328; travel expenses were borne by the grant MM SR 01/35. Research support for M. P. by the U.S. Department of Energy under grant No. DE-FG02-88ER-40388 is acknowledged. The paper was written in its final form at the Institute of Theoretical Physics, Santa Barbara, during the research program Strong Interactions at Finite Temperatures. The authors express gratitude for the warm hospitality extended there and acknowledge the support of the National Science Foundation under Grant No. PHY89-04035.     

The thermodynamic properties of weakly interacting quark-gluon plasma via the one-gluon exchange interaction

The thermodynamic properties of the quark-gluon plasma (QGP), as well as its phase diagram, are calculated as a function of baryon density (chemical potential) and temperature. The QGP is assumed to be composed of the light quarks only, i.e., the up and down quarks, which interact weakly, and the gluons which are treated as they are free. The interaction between quarks is considered in the framework of the one gluon exchange model which is obtained from the Fermi liquid picture. The bag model is used, with fixed bag pressure (B)for the nonperturbative part, and the quantum chromodynamics (QCD) coupling is assumed to be constant, i.e., with no dependence on the temperature or the baryon density. The effect of weakly interacting quarks on the QGP phase diagram are shown and discussed. It is demonstrated that the one-gluon exchange interaction for the massless quarks has considerable effect on the QGP phase diagram and it causes the system to reach to the confined phase at the smaller baryon densities and temperatures. The pressure of excluded volume hadron gas model is also used to find the transition phase diagram. Our results depend on the values of bag pressure and the QCD coupling constant. The latter does not have a dramatic effect on our calculations. Finally, we compare our results with the thermodynamic properties of strange quark matter and the lattice QCD prediction for the QGP transition critical temperature.     

Color-electric conductivity in a viscous quark-gluon plasma

Several different transport processes, such as heat, momentum, and charge transports, may occur simultaneously in a thermal plasma system. The corresponding transport coefficients are heat conductivity, shear viscosity, and electric conductivity. In the present study, we investigate the color-electric conductivity of the quark-gluon plasma(QGP) in the presence of shear viscosity, focusing on the connection between the charge transport and momentum transport. To achieve this goal, we solve the viscous chromohydrodynamic equations obtained from the QGP kinetic theory associated with the distribution function modified by shear viscosity. According to the solved color fluctuations of hydrodynamic quantities, we obtain the induced color current through which the color-electric conductivity is derived. Numerical analysis shows that the conductivity properties of the QGP are mainly demonstrated by the longitudinal part of the color-electric conductivity. Shear viscosity has an appreciable impact on real and imaginary parts of the color-electric conductivity in some frequency regions.     

On diquark clusters in a quark-gluon plasma

An attempt is made to account for the effect of the size of a diquark in exploring the possibility that the pairs of quarks will form diquark clusters in a quark-gluon plasma. It is found that the extended scalar diquarks are distributed more uniformly in the spatial volume than the point diquarks. Although the qualitative features of the pressure-energy density curve remain more or less the same except for small values of energy density, but there appears further lowering of the diquark gas energy in the present case as compared not only to that of the point diquark but also of a free quark gas.     

The hadronisation of a quark-gluon plasma

We consider two scenarios for the expansion of a quark-gluon plasma. If the evolution is slow enough, the system can remain in equilibrium throughout its entire history up to the freeze-out of a hadron gas; for a very rapid expansion, it may break up into hadrons before or at the confinement transition, without ever going through an equilibrium hadron phase. We compare hadron production rates in the two approaches and show that for a hadronisation temperatureT?200 MeV and baryonic chemical potential μ _B ?500 MeV, their predictions essentially coincide. Present data on strange particle production lead to values in this range and hence cannot provide a distinction between the two scenarios. Pion, nucleon and non-strange meson production seem to require a considerably lower freeze-out temperature and baryonic chemical potential. In the hadron gas picture, this is in accord with the difference in mean free path of the different hadrons in the medium; it suggests a sequential freeze-out, in which strange hadrons stop interacting earlier than non-strange hadrons. In the quark-gluon plasma break-up, the hadronic final state fails to provide the high entropy per baryon observed in non-strange hadron production. The break-up moreover leads to a decrease of the entropy per baryon; hence it must be conceptually modified before it can be considered as a viable hadronisation mechanism.     

Heavy hadrons in quark-gluon plasma

We use the nonperturbative quark-antiquark potential derived within the Field Correlator Method and the screened Coulomb potential to calculate binding energies and melting temperatures of heavy mesons and baryons in the deconfined phase of quark-gluon plasma.     

Colored plasmons in a quark-gluon plasma near equilibrium

Within a kinetic theory for QCD plasmas we study the color response function near thermodynamic equilibrium. Its poles yield a longitudinal and a transverse collective mode, both starting at the plasma frequency. Due to the gluon contribution there is no Landau damping for these modes, and creation of gluon or q-$\text{p}$ pairs is the dominant damping mechanism. In an electron plasma the generally quoted Landau damping near threshold is shown to be an artifact of the non-relativistic approximation.