arXiv subjects

Johann Rafelski

Publications and source records attributed to Johann Rafelski.

At least 163 records · Page 9Linked to original sources

arXiv2000

Quark-Gluon Plasma Fireball

Lattice-QCD results provide an opportunity to model, and extrapolate to finite baryon density, the properties of the quark-gluon plasma (QGP). Upon fixing the scale of the thermal coupling constant and vacuum energy to the lattice data, the properties of resulting QGP equations of state (EoS) are developed. We show that the physical properties of the dense matter fireball formed in heavy ion collision experiments at CERN-SPS are well described by the QGP-EoS we presented. We also estimate the properties of the fireball formed in early stages of nuclear collision, and argue that QGP formation must be expected down to 40A GeV in central Pb--Pb interactions.

hep-ph↗

arXiv2000

Sudden Hadronization in Relativistic Nuclear Collisions

We formulate and study a mechanical instability criterion for sudden hadronization of dense matter fireballs formed in 158A GeV Pb--Pb collisions. Considering properties of quark-gluon matter and hadron gas we obtain the phase boundary between these two phases and demonstrate that the required deep QGP supercooling prior to sudden hadronization has occurred.

hep-ph↗

arXiv2000

Electron Positron Annihilation Radiation from SgrA East at the Galactic Center

Maps of the Galactic electron-positron annihilation radiation show evidence for three distinct and significant features: (1) a central bulge source, (2) emission in the Galactic plane, and (3) an enhancement of emission at positive latitudes above the Galactic Center. In this paper, we explore the possibility that Sgr A East, a very prominent radio structure surrounding the Galactic nucleus, may be a significant contributer to the central bulge feature. The motivation for doing so stems from a recently proposed link between this radio object and the EGRET gamma-ray source 2EG J1746-2852. If this association is correct, then Sgr A East is also expected to be a source of copious positron production. The results presented here show that indeed Sgr A East must have produced a numerically significant population of positrons, but also that most of them have not yet had sufficient time to thermalize and annihilate. As such, Sgr A East by itself does not appear to be the dominant current source of annihilation radiation, but it will be when the positrons have cooled sufficiently and they have become thermalized. This raises the interesting possibility that the bulge component may be due to the relics of earlier explosive events like the one that produced Sgr A East.

astro-ph↗

arXiv2000

Free Energy of a Hot Quark-Gluon Plasma

Thermal (Th-)QCD properties appear to disagree with lattice (L-)QCD results, which suggests that Th-QCD does not have a valid perturbative expansion. However, we reproduce L-QCD using the first order $α_s$ corrections in Th-QCD.

hep-ph↗

arXiv2000

B_c Meson Production in Nuclear Collisions at RHIC

We study quantitatively the formation and evolution of B_c bound states in a space-time domain of deconfined quarks and gluons (quark-gluon plasma, QGP). At the Relativistic Heavy Ion Collider (RHIC) one expects for the first time that typical central collisions will result in multiple pairs of heavy (in this case charmed) quarks. This provides a new mechanism for the formation of heavy quarkonia which depends on the properties of the deconfined region. We find typical enhancements of about 500 fold for the B_c production yields over expectations from the elementary coherent hadronic B_c-meson production scenario. The final population of bound states may serve as a probe of the plasma phase parameters.

hep-ph↗

arXiv2000

Observing Quark-Gluon Plasma with Strange Hadrons

We review the methods and results obtained in an analysis of the experimental heavy ion collision research program at nuclear beam energy of 160-200A GeV. We study strange, and more generally, hadronic particle production experimental data. We discuss present expectations concerning how these observables will perform at other collision energies. We also present the dynamical theory of strangeness production and apply it to show that it agrees with available experimental results. We describe strange hadron production from the baryon-poor quark-gluon phase formed at much higher reaction energies, where the abundance of strange baryons and antibaryons exceeds that of nonstrange baryons and antibaryons.

nucl-th↗

arXiv1999

Low-m_t charged pion asymmetry enhancement from hadronization of QGP

We show that in sudden hadronization of QGP a non-equilibrium value of the pion phase space occupancy parameter gamma_q>1 is expected in order to accommodate the entropy excess in QGP and the process of gluon fragmentation. When gamma_q is near to its maximum allowed value, pion overabundance is shown to arise at low $m_\bot$, where the charged pion asymmetry is also amplified. These effects are considered and we show that their magnitude suffices to explain pertinent experimental data obtained in 160-200AGeV Pb- and S- induced reactions.

nucl-th↗

arXiv1999

Expected Production of Strange Baryons and Antibaryons in Baryon-Poor QGP

In a dynamical model of QGP at RHIC we obtain the temporal evolution of strange phase space occupancy at conditions expected to occur in 100+100A GeV nuclear collisions. We show that the sudden QGP break up model developed to describe the SPS experimental results implies dominance of both baryon and antibaryon abundances by the strange baryon and antibaryon yields.

nucl-th↗

arXiv1999

Hadron production in Pb-Pb collisions at 158A GeV

A Fermi statistical model analysis of hadron abundances and spectra obtained in several relativistic heavy ion collision experiments is utilized to characterize a particle source. Properties consistent with a disintegrating, hadron evaporating, deconfined quark-gluon plasma phase fireball are obtained, with a baryochemical potential μ_B=200-210MeV, and a temperature T_f\simeq 140-150MeV, significantly below previous expectations.

nucl-th↗

arXiv1999

Variational Principle for Relativistic Fluid Dynamics

The variational principle for the special and general relativistic hydrodynamics are discussed in view of its application to obtain approximate solutions to these problems. We show that effective Lagrangians can be obtained for suitable ansatz for the dynamical variables such as density profile of the system. As an example, the relativistic version of spherical droplet motion (Rayleigh-Plesset equation) is derived from a simple Lagrangian. For the general relativistic case the most general Lagrangian for spherically symmetric systems is given.

hep-ph↗

arXiv1999

B_c Production at RHIC as a Signal for Deconfinement

The B_C meson is the bound state of b-cbar whose recent detection is the first step toward completion of the spectroscopy of heavy quark mesonic states. The b-c states have properties that conveniently fill the gap between the J/Psi and Upsilon states. Thus it is probable that at RHIC the B_c mesons will serve as a probe of deconfined matter. We find that significant differences arise for B_c formation in deconfined and confined matter. Our initial calculations suggest that: (a) The rates of normal hadronic production mechanisms at RHIC energies are not sufficient to produce a detectable number of B_c mesons, (b) If a region of deconfined quarks and gluons is formed, the production (and survival) rate can be enhanced by several orders of magnitude, and (c) The observation of B_c mesons at RHIC would signal a source of deconfined charmed quarks, and the rate of B_c production will be a measure of the initial density and temperature of that source.

hep-ph↗

arXiv1999

Equilibrium Distribution of Heavy Quarks in Fokker-Planck Dynamics

We obtain within Fokker-Planck dynamics an explicit generalization of Einstein's relation between drag, diffusion and equilibrium distribution for a spatially homogeneous system, considering both the transverse and longitudinal diffusion for dimension n>1. We then provide a complete characterization of when the equilibrium distribution becomes a Boltzmann/J"uttner distribution, and when it satisfies the more general Tsallis distribution. We apply this analysis to recent calculations of drag and diffusion of a charm quark in a thermal plasma, and show that only a Tsallis distribution describes the equilibrium distribution well. We also provide a practical recipe applicable to highly relativistic plasmas, for determining both diffusion coefficients so that a specific equilibrium distribution will arise for a given drag coefficient.

hep-ph↗

arXiv1999

Hadron Freeze-out and QGP Hadronization

Abundances and $m_\bot$-spectra of strange and other hadronic particles emanating from central 158-200 A GeV reactions between nuclei are found to originate from a thermally equilibrated, deconfined source in chemical non-equilibrium. Physical freeze-out parameters and physical conditions (pressure, specific energy, entropy, and strangeness) are evaluated. Five properties of the source we obtain are as expected for direct hadron emission (hadronization) from a deconfined quark-gluon plasma phase.

hep-ph↗

arXiv1998

Chemical Nonequilibrium in High Energy Nuclear Collisions

Strange particles produced in S-Au/W/Pb 200 A GeV and Pb-Pb 158 A GeV reactions are described invoking final hadronic phase space in thermal equilibrium, but allowing chemical non-equilibrium. Several sets of statistical freeze-out parameters are obtained for each system, invoking different models of dense matter. We show that only when allowing for strange and non-strange flavor abundance non-equilibrium, a statistically significant description of the experimental results is obtained. Physical properties of the fireball at chemical freeze-out condition are evaluated and considerable universality of hadron freeze-out between the two different collision systems is established. The relevance of the Coulomb effect in the highly charged Pb-Pb fireballs for the chemical analysis are discussed. The influence of explosive collective matter flow is also described.

hep-ph↗

arXiv1998

Quark-Gluon Plasma in Pb--Pb 158 A GeV collisions: Evidence from strange particle abundances and the Coulomb effect

The hadronic particle production data from relativistic nuclear Pb--Pb 158 A GeV collisions are successfully described within the chemical non-equilibrium model, provided that the analysis treats Omega and anti-Omega abundances with care. We further show that there is a subtle influence of the Coulomb potential on strange quarks in quark matter which is also seen in our data analysis, and this Coulomb effect confirms the finding made by chemical analysis in the S--Au/W/Pb 200 A GeV collisions that the hadron particle source is deconfined with respect to strange quark propagation. Physical freeze-out conditions (pressure, specific energy, entropy, and strangeness) are evaluated and considerable universality of hadron freeze-out between the two different collision systems is established.

hep-ph↗

arXiv1998

Quo Vadis Strangeness? Strangeness - Open Questions

The study of strange and also charmed hadronic particle production in nuclear relativistic collisions offers an opportunity to explore the physical properties of the deconfined quark-gluon phase. We survey the recent accomplishments and the future directions of this research program.

hep-ph↗

arXiv1998

Electromagnetic Fields in the QCD Vacuum

Quarks play an active role in shaping the QCD vacuum structure. Being dual carriers of both `color' and `electric' charges they also respond to externally applied electromagnetic fields. Thus, in principle, the vacuum of strong interactions influences higher order QED processes such as photon-photon scattering. We survey here the current status of the understanding of the vacuum structure of strong interactions, and take a fresh look at its electromagnetic properties.

hep-ph↗

arXiv1998

Chemical non-equilibrium and deconfinement in 200 A GeV Sulphur induced reactions

We interpret hadronic particle abundances produced in S--Au/W/Pb 200 A GeV reactions in terms of the final state hadronic phase space model and determine by a data fit of the chemical hadron freeze-out parameters. Allowing for the flavor abundance non-equilibrium a highly significant fit to experimental particle abundance data emerges, which supports possibility of strangeness distillation. We find under different strategies stable values for freeze-out temperature T_f=143\pm3 MeV, baryochemical potential μ_B= 173\pm6 MeV, ratio of strangeness (γ_s) and light quark (γ_q) phase space occupancies γ_s/γ_q=0.60\pm0.02, and γ_q=1.22\pm0.05 without accounting for collective expansion (radial flow). When introducing flow effects which allow a consistent description of the transverse mass particle spectra, yielding |v_c|=0.49\pm0.01c, we find γ_s/γ_q=0.69\pm0.03, γ_q=1.41\pm0.08. The strange quark fugacity is fitted at λ_s=1.00\pm0.02 suggesting chemical freeze-out directly from the deconfined phase.

hep-ph↗