Johann Rafelski

Strangeness in relativistic heavy ion collisions

Abstract Abundances of strange antibaryons formed in nuclear collisions at above 10 GeV/A are considered as a most accessible diagnostic tool for the study of the possible formation and physical properties of the quark-gluon plasma phase of hadronic matter. In this report we describe the current status and develop a dynamical approach in order to describe strange particle formation in nuclear collisions at high energy.

Enhanced J/{psi} production in deconfined quark matter

In high energy heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven and the Large Hadron Collider at CERN, each central event will contain multiple pairs of heavy quarks. If a region of deconfined quarks and gluons is formed, a mechanism for additional formation of heavy quarkonium bound states will be activated. This is a result of the mobility of heavy quarks in the deconfined region, such that bound states can be formed from a quark and an antiquark that were originally produced in separate incoherent interactions. Model estimates of this effect for J/{psi} production at RHIC indicate that significant enhancements are to be expected. Experimental observation of such enhanced production would provide evidence for deconfinement unlikely to be compatible with competing scenarios.

Strange anti-baryons from quark-gluon plasma

Abstract Experimental results on strange anti-baryon production in nuclear S→W collisions at 200 A GeV are described in terms of a simple model of an explosively disintegrating quark-lepton plasma (QGP). The importance of the strange anti-baryon signal for the identification of the QGP state and for the diagnosis of its properties is demonstrated.

Hot hadronic matter and nuclear collisions

Abstract Based on the statistical bootstrap model of strong interactions, we develop a description of hadronic matter with particular emphasis on hot nuclear matter as created in relativistic heavy ion collisions. We apply our theory to calculate temperatures and average transverse momenta of nucleons and pions from the decay of hadronic fireballs.

Particle Production in Highly Excited Matter

Seven years after the first experiments in the new subfield of nuclear physics known as the highly relativistic heavy ion physics, the NATO Advanced Study Institute on [title] was held at Il Ciocco, near Lucca in Tuscany, Italy. This proceedings volume begins with an overview section (seven lectures

Fermions and bosons interacting with arbitrarily strong external fields

Abstract The question, “What happens to the electron orbitals as the charge of the nucleus is increased without bounds?” has inspired much of the interest in the description of particles bound strongly by external fields. Interest in this problem and in the related Klein paradox extends back nearly to the beginnings of relativistic quantum mechanics. However, the correct interpretation of the theory for overcritical potentials, where the parts of the complete set of single particle solutions associated with particles and antiparticles are no longer distinct, was given only recently. The understanding of the spectrum of the Dirac and Klein-Gordon equations is essential in order to obtain an appropriate physical description with quantum field theory. The strong binding by more than twice the rest mass of the particles in overcritical external potentials leads to qualitatively new effects. In the case of fermions we find spontaneous positron emission accompanied by creation of a charged lowest energy state, i.e. a charged vacuum. The number of positrons produced spontaneously is limited by the Pauli exclusion principle. For bosons we find that depending on the character of the external potential, either neutral or charged Bose condensates develop. While the questions associated with the meson fields seem academic at the moment, the effects attributed to the fermion field stand a good chance of being tested in an experiment in the near future. It is expected that in heavy ion collisions such as uranium on uranium near the Coulomb barrier overcritical electromagnetic fields will be created.

Equilibrium Distribution of Heavy Quarks in Fokker-Planck Dynamics

We obtain an explicit generalization, within Fokker-Planck dynamics, of Einsteins relation between drag, diffusion, and the equilibrium distribution for a spatially homogeneous system, considering both the transverse and longitudinal diffusion for dimension n>1. We provide a complete characterization of the equilibrium distribution in terms of the drag and diffusion transport coefficients. We apply this analysis to charm quark dynamics in a thermal quark-gluon plasma for the case of collisional equilibration.

Electron shells in over-critical external fields

When the charge of a nucleus exceedsZ=Zcr≈ 164–172 the energy of the 1s-electron level is lowered beyond the critical value of −mec2. Then this bound level is degenerated with negative energy continuum solutions of the Dirac equation and becomes a resonance, whose shape varies and is approximately of Breit-Wigner type forZ−Zcr≳5. The physical meaning of this resonance can be understood most easily if the 1s-level is unoccupied (K-hole). In this case a positron may escape ifZ>Zcr, a process, that can be interpreted as auto-ionization of the positron. This fundamentally new process of quantum electrodynamics of strong fields can be tested experimentally by scattering very heavy ions (Z≧80) on each other since in such collisions superheavy electronic molecules occur (superheavy quasimolecules).

Solution of the Dirac equation with two Coulomb centres

Abstract The Dirac equation for a relativistic particle (electron) in the field of two Coulomb centres Z 1 and Z 2 — pointlike as well as extended charges — has been solved. The systems BrBr, IAu, UU are shown as examples.

Auto-ionization of positrons in heavy ion collisions

Autoionization of positrons occurs as a fundamentally new process of quantum electrodynamics, if empty 1s- or 2p1/2− etc. electronic shells obtain binding energies larger than 2mec2. This effect should be experimentally observable in the scattering of very heavy ions (Z≧80) on each other since in such collisions superheavy electronic molecules are formed (superheavy quasi-molecules). The scattering mechanism and the distribution of autoionization positrons are discussed. The adiabaticity of the heavy ion collision is studied and the electron-positron pair production background to the ionization problem is estimated. Analytic solutions are obtained for 1/r-potentials for the caseZα≧1. The phase shifts of negative energy solutions in the case of cutoff Coulomb potentials reveal the accuracy of the autoionization formalism.