Projected Three-Pion Correlation Functions

We propose a new procedure for constructing projected three-pion correlation functions which reduces undesirable artificial momentum dependences resulting from the commonly used procedure and facilitates comparison of three-pion correlation data with theoretical models.Comment: 6 pages revtex, incl. 1 figure. Submitted as Brief Report to Physical Review C. Normalization error and typos correcte

Bulk Viscosity driven clusterization of quark-gluon plasma and early freeze-out in relativistic heavy-ion collisions

We introduce a new scenario for heavy ion collisions that could solve the lingering problems associated with the so-called HBT puzzle. We postulate that the system starts expansion as the perfect quark-gluon fluid but close to freeze-out it splits into clusters, due to a sharp rise of bulk viscosity in the vicinity of the hadronization transition. We then argue that the characteristic cluster size is determined by the viscosity coefficient and the expansion rate. Typically it is much smaller and independent of the total system volume. These clusters maintain the pre-existing outward-going flow, as a spray of droplets, but develop no flow of their own, and hadronize by evaporation. We provide an ansatz for converting the hydrodynamic output into clusters.Comment: Accepted for publication, Phys. Rev. C. Arguments considerably expanded, refined and reworde

Strangeness Balance in HADES Experiments and the Xi- Enhancement

HADES data on a strangeness production in Ar+KCl collisions at 1.76A GeV are analyzed within a minimal statistical model. The total negative strangeness content is fixed by the observed K^+ multiplicities on event-by-event basis. Particles with negative strangeness are assumed to remain in chemical equilibrium with themselves and in thermal equilibrium with the environment until a common freeze-out. Exact strangeness conservation in each collision event is explicitly preserved. This implies that Xi baryons can be released only in events where two or more kaons are produced. An increase of the fireball volume due to application of a centrality trigger in HADES experiments is taken into account. We find that experimental ratios of K-/K+, Lambda/K+ and Sigma/K+ can be satisfactorily described provided in-medium potentials are taken into account. However, the calculated Xi-/Lambda/K+ ratio proves to be significantly smaller compared to the measured value (8 times lower than the experimental median value and 3 times lower than the lower error bar). Various scenarios to explain observed Xi enhancement are discussed. Arguments are given in favor of the Xi production in direct reactions. The rates of the possible production processes are estimated and compared.Comment: 13 pages, 3 figure

The freeze-out mechanism and phase-space density in ultrarelativistic heavy-ion collisions

We explore the consequences of a freeze-out criterion for heavy-ion collisions, based on pion escape probabilities from the hot and dense but rapidly expanding collision region. The influence of the expansion and the scattering rate on the escape probability is studied. The temperature dependence of this scattering rate favors a low freeze-out temperature of ~100 MeV. In general, our results support freeze-out along finite four-volumes rather than sharp three-dimensional hypersurfaces, with high-pt particles decoupling earlier from smaller volumes. We compare our approach to the proposed universal freeze-out criteria using the pion phase-space density and its mean free path.Comment: 8 pages, 2 figures, although conclusions are unchanged, the paper has been re-written and the title has been changed for the sake of better presentatio

Universal Pion Freeze-out Phase-Space Density

Results on the pion freeze-out phase-space density in sulphur-nucleus, Pb-Pb and pion-proton collisions at CERN-SPS are presented. All heavy-ion reactions are consistent with the thermal Bose-Einstein distrtibution f=1/(exp(E/T)-1) at T~120 MeV, modified for expansion. Pion-proton data are also consistent with f, but at T~180 MeV.Comment: 1 page, 1 figure; 98' report for GSI-Darmstad

HBT radii from the multipole Buda-Lund model

The Buda-Lund model describes an expanding hydrodynamical system with ellipsoidal symmetry and fits the observed elliptic flow and oscillating HBT radii successfully. The ellipsoidal symmetry can be characterized by the second order harmonics of the transverse momentum distribution, and it can be also observed in the azimuthal oscillation of the HBT radii measured versus the second order reaction plane. The model may have to be changed to describe the experimentally indicated higher order asymmetries. In this paper we detail an extension of the Buda-Lund hydro model to investigate higher order flow harmonics and the triangular dependence of the azimuthally sensitive HBT radii

Higher order anisotropies in the Buda-Lund model -- disentangling flow and density field anisotropies

The Buda-Lund hydro model describes an expanding ellipsoidal fireball, and fits the observed elliptic flow and oscillating HBT radii successfully. Due to fluctuations in energy depositions, the fireball shape however fluctuates on an event-by-event basis. The transverse plane asymmetry can be translated into a series of multipole anisotropy coefficients. These anisotropies then result in measurable momentum-space anisotropies, to be measured with respect to their respective symmetry planes. In this paper we detail an extension of the Buda-Lund model to multipole anisotropies and investigate the resulting flow coefficients and oscillations of HBT radii

Lifetimes and Sizes from Two-Particle Correlation Functions

We discuss the Yano-Koonin-Podgoretskii (YKP) parametrization of the two-particle correlation function for azimuthally symmetric expanding sources. We derive model-independent expressions for the YKP fit parameters and discuss their physical interpretation. We use them to evaluate the YKP fit parameters and their momentum dependence for a simple model for the emission function and propose new strategies for extracting the source lifetime. Longitudinal expansion of the source can be seen directly in the rapidity dependence of the Yano-Koonin velocity.Comment: 15 pages REVTEX, 2 figures included, submitted to Phys. Lett. B, Expanded discussion of disadvantages of standard HBT fit and of Fig.

Observable implications of geometrical and dynamical aspects of freeze-out in heavy ion collisions

Using an analytical parameterization of hadronic freeze-out in relativistic heavy ion collisions, we present a detailed study of the connections between features of the freeze-out configuration and physical observables. We focus especially on anisotropic freeze-out configurations (expected in general for collisions at finite impact parameter), azimuthally-sensitive HBT interferometry, and final-state interactions between non-identical particles. Model calculations are compared with data taken in the first year of running at RHIC; while not perfect, good agreement is found, raising the hope that a consistent understanding of the full freeze-out scenario at RHIC is possible, an important first step towards understanding the physics of the system prior to freeze-out.Comment: 36 pages, 56 figures, 2 tables; version accepted for publication in PRC: some figures, references and discussion added; now also discusses classical versus quantum statistic

Strangeness production time and the K+/pi+ horn

We construct a hadronic kinetic model which describes production of strange particles in ultrarelativistic nuclear collisions in the energy domain of SPS. We test this model on description of the sharp peak in the excitation function of multiplicity ratio K+/pi+ and demonstrate that hadronic model reproduces these data rather well. The model thus must be tested on other types of data in order to verify the hypothesis that deconfinement sets in at lowest SPS energies.Comment: proceedings of Hot Quarks 0