Impact of baryon resonances on the chiral phase transition at finite temperature and density

We study the phase diagram of a generalized chiral SU(3)-flavor model in mean-field approximation. In particular, the influence of the baryon resonances, and their couplings to the scalar and vector fields, on the characteristics of the chiral phase transition as a function of temperature and baryon-chemical potential is investigated. Present and future finite-density lattice calculations might constrain the couplings of the fields to the baryons. The results are compared to recent lattice QCD calculations and it is shown that it is non-trivial to obtain, simultaneously, stable cold nuclear matter.Comment: 18 pages, 7 figure

Inhomogeneous freeze-out in relativistic heavy-ion collisions

A QCD phase transition may reflect in a inhomogeneous decoupling surface of hadrons produced in relativistic heavy-ion collisions. We show that due to the non-linear dependence of the particle densities on the temperature and baryon-chemical potential such inhomogeneities should be visible even in the integrated, inclusive abundances. We analyze experimental data from Pb+Pb collisions at CERN-SPS and Au+Au collisions at BNL-RHIC to determine the amplitude of inhomogeneities.Comment: 8 pages, 5 figure

In-medium vector meson masses in a Chiral SU(3) model

A significant drop of the vector meson masses in nuclear matter is observed in a chiral SU(3) model due to the effects of the baryon Dirac sea. This is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation. The appreciable decrease of the in-medium vector meson masses is due to the vacuum polarisation effects from the nucleon sector and is not observed in the mean field approximation.Comment: 26 pages including 10 figures; the text has been modified for clarit

Critical Review Of Quark Gluon Plasma Signals

Compelling evidence for a new form of matter has been claimed to be formed in Pb+Pb collisions at SPS. We critically review two suggested signatures for this new state of matter: First the suppression of the J/$\Psi$, which should be strongly suppressed in the QGP by two different mechanisms, the color-screening and the QCD-photoeffect. Secondly the measured particle, in particular strange hadronic, ratios might signal the freeze-out from a quark-gluon phase.Comment: 7 pages 6 figures, Contribution to the Proceedings of CRIS 2000, 3rd Catania Relativistic Ion Studies, Acicastello, Italy, May 22-26, 200

Particle ratios at RHIC: Effective hadron masses and chemical freeze-out

The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU(3) \sigma-\omega approach. The commonly adopted noninteracting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. Contrary, the chiral SU(3) model predicts temperature and density dependent effective hadron masses and effective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three different parametrizations of the model, which show different types of phase transition behaviour, are investigated. We show that if a chiral phase transition occured in those collisions, ''freezing'' of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking. Furthermore, the extracted chemical freeze-out parameters differ considerably from those obtained in simple noninteracting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The in-medium masses turn out differ up to 150 MeV from their vacuum values.Comment: 13 pages, 4 figure

Effects of Dirac sea polarization on hadronic properties - A chiral SU(3) approach

The effect of vacuum fluctuations on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization. The effect of the baryon Dirac sea is seen to modify hadronic properties and in contrast to a calculation in mean field approximation it is seen to give rise to a significant drop of the vector meson masses in hot and dense matter. This effect is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation (RHA), where the baryon self energy is modified due to interactions with both the non-strange $(\sigma)$ and the strange $(\zeta)$ scalar fields.Comment: 25 pages including 13 figures,figure styles modified,few clarifying sentences added in text, to appear in Phys. Rev.

Hypermatter in chiral field theory

We investigate the properties of hadronic matter and nuclei be means of a generalized $SU(3)\times SU(3)$ $\sigma$ model with broken scale invariance. In mean-field approximation, vector and scalar interactions yield a saturating nuclear equation of state. Finite nuclei can be reasonably described, too. The condensates and the effective baryon masses at finite baryon density and temperature are discussed.Comment: uses IOP style, to be published in Journal of Physics, Proceedings of the International Symposium on Strangeness in Quark Matter 1997, April 14-18, Thera (Santorini), Hella

Current Status of Quark Gluon Plasma Signals

Compelling evidence for the creation of a new form of matter has been claimed to be found in Pb+Pb collisions at SPS. We discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions. It is demonstrated that so far none of the proposed signals like J\psi meson production/suppression, strangeness enhancement, dileptons, and directed flow unambigiously show that a phase of deconfined matter has been formed in SPS Pb+Pb collisions. We emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from data.Comment: 12 pages, 6 figures, Proceedings of the Symposium on Fundamental Issues in Elementary Matter In Honor and Memory of Michael Danos 241. WE-Heraeus-Seminar Bad Honnef, Germany, 25--29 September 2000. To appear in Heavy Ion Phy

Following carbon condensation by in-situ TEM : towards a rational understanding of the processes in the synthesis of nitrogen-doped carbonaceous materials.

Porous carbonaceous materials obtained from biomass have been an important class of CO2 sorbents since ancient times. Recent progress in carbon-based adsorbent technology is based on the implication of the concept of heteroatom doping. In this respect, the synthesis of carbonaceous materials through one-step condensation of cheap nitrogen-containing molecular precursors is an attractive strategy for obtaining such N-doped carbons. The design of the adsorbents obtained by this route relies on the careful adjustment of synthesis parameters, such as the temperature, the heating rate, and the atmosphere. However, in most cases, the latter's choice remains rather empirical due to the lack of a fundamental understanding of the condensation mechanism of molecular precursors. In this work, we followed the structural, morphological, and chemical evolution of a molecular precursor (uric acid) at the nanoscale using a combination of in-situ condensation inside a scanning transmission electron microscope with ex-situ analysis of the products of condensation at different temperatures, atmospheres, and heating rates, and correlate our findings with the CO2 sorption properties of the obtained materials. We showed that varying pressures and reaction rates result in particles with different porosity. The porosity of the surface of the particles during the early stages of condensation governs the subsequent release of volatiles and the development of a hierarchical pore structure. We found that synthesis in vacuum enables effective condensation at considerably low temperatures (500 °C). Using a higher heating rate (10 °C/min) suppresses structural ripening and preserves the optimal size of micropores, thus giving a CO2 uptake twice as high compared to samples synthesized in nitrogen atmosphere, which is commonly used, preserving the same selectivity.ER