Mark I. Gorenstein

Onset of deconnement in nucleus-nucleus collisions: Review for pedestrians and experts

Evidence for the energy threshold of creating the quark-gluon plasma in nucleusnucleus collisions, the so-called onset of deconnement, has been found by the energy scan program of the NA49 experiment at the CERN SPS. In this paper we review the experimental and theoretical status of this phenomenon. First, the basic, qualitative ideas are presented for non-experts. Next, the latest experimental results are compared to a statistical model within which the onset of deconnement and its signals had been predicted. Finally, alternative interpretations and open questions are discussed.

Transverse activity of kaons and deconfinement phase transition in nucleus–nucleus collisions

Abstract We found that the experimental results on transverse mass spectrum of kaons produced in central Pb+Pb (Au+Au) collisions show an anomalous dependence on the colliding energy. The inverse slope of the spectrum increases with the energy in the low (AGS) and high (RHIC) energy domains, whereas it remains constant in the intermediate (SPS) energy range. We argue that this anomaly is probably caused by the modification of the equation of state in the transition region between confined and deconfined matter. This observation may be considered as a new signal, in addition to the previously reported anomalies in the pion and strangeness production, of the onset of deconfinement located in the low SPS energy domain.

Equation of State, Spectra and Composition of Hot and Dense Infinite Hadronic Matter in a Microscopic Transport Model ∗

Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine(February 9, 2008)Equilibrium properties of infinite relativistic hadron matter are investi-gated using the Ultrarelativistic Quantum Molecular Dynamics (UrQMD)model. The simulations are performed in a box with periodic boundary con-ditions. Equilibration times depend critically on energy and baryon densities.Energy spectra of various hadronic species are shown to be isotropic andconsistent with a single temperature in equilibrium. The variation of energydensity versus temperature shows a Hagedorn-like behavior with a limitingtemperature of 130±10 MeV. Comparison of abundances of different particlespecies to ideal hadron gas model predictions show good agreement only ifdetailed balance is implemented for all channels. At low energy densities,high mass resonances are not relevant; however, their importance raises withincreasing energy density. The relevance of these different conceptual frame-works for any interpretation of experimental data is questioned.

van der Waals Interactions in Hadron Resonance Gas: From Nuclear Matter to Lattice QCD

An extension of the ideal hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters a and b are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within the VDW-HRG model. Compared to the ideal HRG model, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of second and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region T∼140-190  MeV. For many observables this behavior resembles closely the results obtained from lattice QCD simulations. This hadronic model also predicts nontrivial behavior of net-baryon fluctuations in the region of phase diagram probed by heavy-ion collision experiments. These results imply that VDW interactions play a crucial role in the thermodynamics of hadron gas. Thus, the commonly performed comparisons of the ideal HRG model with the lattice and heavy-ion data may lead to misconceptions and misleading conclusions.

Bose-Einstein condensation of pions in high multiplicity events

Abstract We present microcanonical ensemble calculations of particle number fluctuations in the ideal pion gas approaching Bose–Einstein condensation. At high collision energy, in the samples of events with a fixed number of all pions, N π , one may observe a prominent signal. When N π increases the scaled variances for particle number fluctuations of both neutral and charged pions increase dramatically in the vicinity of the Bose–Einstein condensation line. As an example, the estimates are presented for p + p collisions at the beam energy of 70 GeV.

Particle number fluctuations in high-energy nucleus-nucleus collisions from microscopic transport approaches

Event-by-event multiplicity fluctuations in nucleus-nucleus collisions are studied within the hadron-string dynamics (HSD) and ultra-relativistic quantum molecular dynamics (UrQMD) transport models. The scaled variances of negative, positive, and all charged hadrons in Pb+Pb at 158A GeV are analyzed in comparison to the data from the NA49 Collaboration. We find a dominant role of the fluctuations in the nucleon participant number for the final hadron multiplicity fluctuations. This fact can be used to check different scenarios of nucleus-nucleus collisions by measuring the final multiplicity fluctuations as a function of collision centrality. The analysis reveals surprising effects in the recent NA49 data which indicate a rather strong mixing of the projectile and target hadron production sources even in peripheral collisions.

Power law in a microcanonical ensemble with scaling volume fluctuations

Volume fluctuations are introduced in a statistical modeling of relativistic particle collisions. The microcanonical ensemble is used, and the volume fluctuations are assumed to have specific scaling properties. This leads to the KNO scaling of the particle multiplicity distributions as measured in p + p interactions. A striking prediction of the model is a power law form of the single particle momentum spectrum at high momenta. Moreover, the mean multiplicity of heavy particles also decreases as a function of the particle mass according to a power law. Finally, it is shown that the dependence of the momentum spectrum on the particle mass and momentum reduces to the dependence on the particle energy. These results resemble the properties of particle production in collisions of high energy particles.

Viscosity in the excluded volume hadron gas model

The shear viscosity \ensuremath{\eta} in the van der Waals excluded volume hadron-resonance gas model is considered. For the shear viscosity the result of a nonrelativistic gas of hard-core particles is extended to a mixture of particles with different masses but equal values of hard-core radius

Multiplicity fluctuations in hadron-resonance gas

r

Pion multiplicity in heavy-ion collisions: possible signature of the deconfinement transition

. The relativistic corrections to hadron average momenta in thermal equilibrium are also taken into account. The ratio of the viscosity \ensuremath{\eta} to the entropy density