E. Molnar

Covariant description of kinetic freeze-out through a finite time-like layer

The freeze-out (FO) problem is addressed for a covariant FO probability and a finite FO layer with a time-like normal vector continuing the line of studies introduced in Molnar et al (2006 Phys. Rev. C 74 024907). The resulting post-FO momentum distribution functions are presented and discussed. We show that in general the post-FO distributions are non-thermal and asymmetric distributions even for time-like FO situations.

Modified Boltzmann Transport Equation

Recently several works have appeared in the literature in which authors try to describe Freeze Out (FO) in energetic heavy ion collisions based on the Boltzmann Transport Equation (BTE). The aim of this work is to point out the limitations of the BTE, when applied for the FO modeling, and to propose the way how the BTE approach can be generalized for the very fast processes.

Freeze-out of the expanding system

Abstract.The freeze-out (FO) of the expanding systems, created in relativistic heavy-ion collisions, is discussed. We start with kinetic FO model, which realizes complete physical FO in a layer of given thickness, and then combine our gradual FO equations with Bjorken-type system expansion into a unified model. We shall see that the basic FO features, pointed out in the earlier works, are not smeared out by the expansion.

Modified Boltzmann Transport Equation and Freeze Out

Abstract.We study the Freeze-Out process in high-energy heavy-ion reaction. The description of the process is based on the Boltzmann Transport Equation (BTE). We point out the basic limitations of the BTE approach and introduce the Modified BTE. The Freeze-Out dynamics is presented in the 4-dimensional space-time in a layer of finite thickness, and we employ the Modified BTE for the realistic Freeze-Out description.

Covariant kinetic freeze-out description through a finite space-time layer

The problem of freeze-out (FO) in high energy heavy ion reactions is addressed. We develop and analyze a covariant FO description valid for a finite space-time layer.

Freeze-out in narrow and wide layers

The freeze-out of particles from a layer of finite thickness is discussed in a phenomenological kinetic model. The proposed model, based on the Modified Boltzman Transport Equation, is Lorentz invariant and can be applied equally well for the freeze-out layers with space-like and time-like normal vectors. It leads to non-equilibrated post freeze-out distributions. The dependence of the resulting distribution on the thickness of the layer is presented and discussed for a space-like freeze-out scenario.

The 3rd Flow Component as a QGP Signal

Earlier fluid dynamical calculations with QGP show a softening of the directed flow while with hadronic matter this effect is absent. On the other hand, we indicated that a third flow component shows up in the reaction plane as an enhanced emission, which is orthogonal to the directed flow. This is not shadowed by the deflected projectile and target, and shows up at measurable rapidities, y CM=1−2. To study the formation of this effect initial stages of relativistic heavy ion collisions are studied. An effective string rope model is presented for heavy ion collisions at RHIC energies. Our model takes into account baryon recoil for both target and projectile, arising from the acceleration of partons in an effective field. The typical field strength (string tension) for RHIC energies is about 5–12 GeV/fm, what allows us to talk about “string ropes”. The results show that QGP forms a tilted disk, such that the direction of the largest pressure gradient stays in the reaction plane, but deviates from both the beam and the usual transverse flow directions. The produced initial state can be used as an initial condition for further hydrodynamical calculations. Such initial conditions lead to the creation of third flow component. Recent v 1 measurements are promising that this effect can be used as a diagnostic tool of the QGP.

Modelling of Boltzmann transport equation for freeze-out

The freeze-out (FO) in high-energy heavy-ion collisions is assumed to be continuous across finite layer in space–time. Particles leaving local thermal equilibrium start to freeze out gradually till they leave the layer, where all the particles are frozen out. To describe such a kinetic process we start from Boltzmann transport equation (BTE). However, we will show that the basic assumptions of BTE, such as molecular chaos or spatial homogeneity do not hold for the above-mentioned FO process. The aim of the presented work is to analyse the situation, discuss the modification of BTE and point out the physical causes, which yield to these modifications of BTE for describing FO.

Impact of nucleon mass shift on the freeze-out process

The freeze out of a massive nucleon gas through a finite layer with time-like normal is studied. The impact of in-medium nucleon mass shift on the freeze out process is investigated. A considerable modification of the thermodynamical variables temperature, flow-velocity, energy density and particle density has been found. Due to the nucleon mass shift the freeze out particle distribution functions are changed noticeably in comparison with evaluations, which use vacuum nucleon mass.

Phase Transitions in High Energy Heavy-Ion Collisions

Modelling Quark-Gluon Plasma formation and decay in high energy heavy ion reactions is presented in a framework of a multi-module setup. The collective features, governing the equlibrated fluid dynamical stages of the model are emphasized. Flow effects formed from the initial conditions are discussed. Particular attention is given to the improvement of the final hadronization and freeze-out part of the reaction which has strong effects on the observables.