Transition from a quark-gluon plasma in the presence of a sharp front

The effect of a sharp front separating the quarkgluon plasma phase from the hadronic phase is investigated. Energy-momentum conservation and baryon number conservation constrain the possible temperature jump across the front. If one assumes that the temperature in the hadronic phase isT200 MeV, as has been suggested by numerous results from relativistic ion collisions, one can determine the corresponding temperature in the quark phase with the help of continuity equations across the front. The calculations reveal that the quark phase must be in a strongly supercooled state. The stability of this solution with respect to minor modifications is investigated. In particular the effect of an admixture of hadronic matter in the quark phase (e.g. in the form of bubbles) is considered in detail. In the absence of admixture the transition proceeds via a detonation transition and is accompanied by a substantial super-cooling of the quark-gluon plasma phase. The detonation is accompanied by less supercooling if a small fraction of bubbles is allowed. By increasing the fraction of bubbles the supercooling becomes weaker and eventually the transition proceeds via a smoother deflagration wave.     

Charged particle ratio fluctuation as a signal for quark-gluon plasma

Modern data are showing increasing evidence that the Universe is accelerating. So far, all attempts to account for the acceleration have required some fundamental dimensionless quantities to be extremely small. We show how a class of scalar field models (which may emerge naturally from superstring theory) can account for acceleration which starts in the present epoch with all the potential parameters O(1) in Planck units.     

FastJ/Ψ's as a signal for quark-gluon plasma formation

The weak production of a top particle of mass ?35 GeV is seen to be an order of magnitude lower than the most conservative estimate of strong production, and two orders of magnitude lower than the rate required to explain the UA1 single jet electron events. All the kinematic distributions are very similar for the two production mechanisms. Detailed comparison of the rate and kinematic distributions are shown, for the decay electron (muon)p _T cut of 10 and 15 GeV.     

Hydrodynamics of a quark-gluon plasma undergoing a phase transition

We present a new method for solving the relativistic hydrodynamic equations. This method allows a simple and reliable numerical treatment of shock waves. We check its accuracy in one-dimensional problems for which analytical solutions are known. Then we apply it to a 3-dimensional calculation of the evolution of a quark-gluon plasma, assuming cylindrical symmetry and longitudinal boost invariance. We treat the hadronization as a first-order phase transition and study the effects of this phase transition on the final distributions of particles. In particular, we analyse the possible correlations between particle multiplicities and transverse momenta which might signal the occurrence of such a phase transition in heavy ion collisions.     

Searching photon signal of quark-gluon plasma formation

The intensive radiation of magnetic bremsstrahlung type resulting from interaction of escaping quarks with the collective colour field ensuring the confinement and bringing back quarks into plasma is discussed as a new possible signal of quark-gluon plasma formation.     

Are cumulative particles a signal of quark-gluon plasma formation?

An analysis of the spectra of cumulative particles within the framework of the limiting fragmentation I model shows that a droplet of quark-gluon plasma moving through a nucleus can be their source.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 93–97, August, 1989.The author is deeply grateful for discussions with N. P. Zotov, L. M. Slad', Yu. T. Kiselev, L. V. Fil'kov, and V. A. Tsarev.     

Effect of colour singletness of quark-gluon plasma in quark-hadron phase transition

Consequences of the constraint of SU(3) colour singletness of quark-gluon plasma are studied. This restriction increases the free energy barrier for the formation of hadronic bubble in supercooled phase and influences significantly the dynamics of the initial stage of quark-hadron phase transition. It also introduces terms dependent on the volume occupied by the plasma in the energy density and the pressure. These modifactions vanish in the limit of an infinite volume. The last stage of the hadronization of the QGP likely to be formed in relativistic heavy ion collisions is necessarily characterized by a decreasing volume containing the quark matter, and thus these corrections become important. The nucleation of plasma droplets at AGS energies is also seen to be strongly affected by the requirement of colour singletness, and the choice of prefactor. Received: 4 December 1997 / Published online: 15 May 1998     

Constraints for critical temperature of the phase transition into the quark-gluon plasma

Low temperature of the phase transition into the quark-gluon plasma correspond to low values of the bag model constant and to absolutely stable strange quark matter. Some of the observed pulsars are identified quite reliably as neutron stars. If strange matter is stable, the central density of these pulsars is to be smaller that critical density of the phase transition into the nonstrange quark matter. The nonstrange quark matter being formed turns to more stable strange matter on a weak interaction timescale converting neutron stars into strange stars. The requirement of stability of old and newly born neutron stars is used to constrain the bag model constant and the critical temperature of the phase transition into the quark-gluon plasma at zero chemical potential.     

Flow at the SPS and RHIC as a quark-gluon plasma signature

Radial and elliptic flow in noncentral heavy-ion collisions can constrain the effective equation of state (EOS) of the excited nuclear matter. To this end, a model combining relativistic hydrodynamics and a hadronic transport code [Sorge, Phys. Rev. C 52, 3291 (1995)] is developed. For an EOS with a first-order phase transition, the model reproduces both the radial and elliptic flow data at the SPS. With the EOS fixed from SPS data, we quantify predictions at RHIC where the quark-gluon plasma (QGP) pressure is expected to drive additional radial and elliptic flows. Currently, the strong elliptic flow observed in the first RHIC measurements does not conclusively signal this nascent QGP pressure.     

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.     

Tagged jets and jet reconstruction as a probe of the quark-gluon plasma

The large center-of-mass energies available to the heavy-ion program at the LHC and recent experimental advances at RHIC will enable QCD matter at very high temperatures and energy densities, that is, the quark-gluon plasma (QGP), to be probed in unprecedented ways. Fully-reconstructed inclusive jets and the away-side hadron showers associated with electroweak bosons, that is, tagged jets, are among these exciting new probes. Full jet reconstruction provides an experimental window into the mechanisms of quark and gluon dynamics in the QGP which is not accessible via leading particles and leading particle correlations. Theoretical advances in these exciting new fields of research can help resolve some of the most controversial points in heavy ion physics today such as the significance of the radiative, collisional and dissociative processes in the QGP and the applicability of strong versus weak coupling regimes to describe jet production and propagation. In this proceedings, I will present results on the production and subsequent suppression of high energy jets tagged with Z bosons in relativistic heavy-ion collisions at RHIC and LHC energies using the Gyulassy-Levai-Vitev (GLV) parton energy loss approach.