33 research outputs found
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