166 research outputs found
Entropy production by resonance decays
We investigate entropy production for an expanding system of particles and
resonances with isospin symmetry -- in our case pions and mesons --
within the framework of relativistic kinetic theory. A cascade code to simulate
the kinetic equations is developed and results for entropy production and
particle spectra are presented.Comment: 17 pages, 10 ps-figures included, only change: preprint number adde
A systematic comparison of jet quenching in different fluid-dynamical models
Comparing four different (ideal and viscous) hydrodynamic models for the
evolution of the medium created in 200 AGeV Au-Au collisions, combined with two
different models for the path length dependence of parton energy loss, we study
the effects of jet quenching on the emission-angle dependence of the nuclear
suppression factor R_AA(phi) and the away-side per trigger yield I_AA(phi).
Each hydrodynamic model was tuned to provide a reasonable description of the
single-particle transverse momentum spectra for all collision centralities, and
the energy loss models were adjusted to yield the same pion nuclear suppression
factor in central Au-Au collisions. We find that the experimentally measured
in-plane vs. out-of-plane spread in R_AA(phi) is better reproduced by models
that shift the weight of the parton energy loss to later times along its path.
Among the models studied here, this is best achieved by energy loss models that
suppress energy loss at early times, combined with hydrodynamic models that
delay the dilution of the medium density due to hydrodynamic expansion by
viscous heating. We were unable to identify a clear tomographic benefit of a
measurement of I_AA(phi) over that of R_AA(phi).Comment: 17 pages, 11 figure
Rapidity particle spectra in sudden hadronization of QGP
We show that the remaining internal longitudinal flow of colliding quarks in
nuclei offers a natural explanation for the diversity of rapidity spectral
shapes observed in Pb--Pb 158AGeV nuclear collisions. Thus QGP sudden
hadronization reaction picture is a suitable approach to explain the rapidity
spectra of hadrons produced.Comment: 3 pages including 2 figure
Two-particle interferometry for non-central heavy-ion collisions
In non-central heavy ion collisions, identical two particle
Hanbury-Brown/Twiss (HBT) correlations C(K,q) depend on the azimuthal direction
of the pair momentum K. We investigate the consequences for a harmonic analysis
of the corresponding HBT radius parameters. Our discussion includes both, a
model- independent analysis of these parameters in the Gaussian approximation,
and the study of a class of hydrodynamical models which mimic essential
geometrical and dynamical properties of peripheral heavy ion collisions. Also,
we discuss the additional geometrical and dynamical information contained in
the harmonic coefficients of these HBT radius parameters. The leading
contribution of their first and second harmonics are found to satisfy simple
constraints. This allows for a minimal, azimuthally sensitive parametrization
of all first and second harmonic coefficients in terms of only two additional
fit parameters. We determine to what extent these parameters can be extracted
from experimental data despite finite multiplicity fluctuations and the
resulting uncertainty in the reconstruction of the reaction plane.Comment: 14 pages, RevTeX, 7 eps-figures include
The inverse Laplace transform as the ultimate tool for transverse mass spectra
New high statistics data from the second generation of ultrarelativistic
heavy-ion experiments open up new possibilities in terms of data analysis. To
fully utilize the potential we propose to analyze the -spectra of
hadrons using the inverse Laplace transform. The problems with its inherent
ill-definedness can be overcome and several applications in other fields like
biology, chemistry or optics have already shown its feasability. Moreover, the
method also promises to deliver upper bounds on the total information content
of the spectra, which is of big importance for all other means of analysis.
Here we compute several Laplace inversions from different thermal scenarios,
both analytically and numerically, to test the efficiency of the method.
Especially the case of a two component structure, related to a possible first
order phase transition to a quark gluon plasma, is closer investigated and it
is shown that at least a signal to noise ratio of is necessary to
resolve two individual components.Comment: 13 pages (PostScript, including figures), BNL-NTHES
Resonance contributions to HBT correlation radii
We study the effect of resonance decays on intensity interferometry for heavy
ion collisions. Collective expansion of the source leads to a dependence of the
two-particle correlation function on the pair momentum K. This opens the
possibility to reconstruct the dynamics of the source from the K-dependence of
the measured HBT radii. Here we address the question to what extent resonance
decays can fake such a flow signal. Within a simple parametrization for the
emission function we present a comprehensive analysis of the interplay of flow
and resonance decays on the one- and two-particle spectra. We discuss in detail
the non-Gaussian features of the correlation function introduced by long-lived
resonances and the resulting problems in extracting meaningful HBT radii. We
propose to define them in terms of the second order q-moments of the correlator
C(q, K). We show that this yields a more reliable characterisation of the
correlator in terms of its width and the correlation strength `lambda' than
other commonly used fit procedures. The normalized fourth-order q-moments
(kurtosis) provide a quantitative measure for the non-Gaussian features of the
correlator. At least for the class of models studied here, the kurtosis helps
separating effects from expansion flow and resonance decays, and provides the
cleanest signal to distinguish between scenarios with and without transverse
flow.Comment: 23 pages, twocolumn RevTeX, 12 eps-figures included, minor changes
following referee comment
Hydrodynamics near the QCD Phase Transition: Looking for the Longest-Lived Fireball
We propose a new strategy for the experimental search of the QCD phase
transition in heavy ion collisions: One may tune collision energy around the
point where the lifetime of the fireball is expected to be longest. We
demonstrate that the hydrodynamic evolution of excited nuclear matter does
change dramatically as the initial energy density goes through the "softest
point" (where the pressure to energy density ratio reaches its minimum). For
our choice of equation of state, this corresponds to epsilon_i approx. = 1.5
GeV/fm^3 and collision energy E_lab/A approx. = 30 GeV (for Au+Au). Various
observables seem to show distinct changes near the softest point.Comment: 7 pages, 3 Postscript figures (tar compressed and uuencoded)
submitte
Hydrodynamical assessment of 200 AGeV collisions
We are analyzing the hydrodynamics of 200 A GeV S+S collisions using a new
approach which tries to quantify the uncertainties arising from the specific
implementation of the hydrodynamical model. Based on a previous
phenomenological analysis we use the global hydrodynamics model to show that
the amount of initial flow, or initial energy density, cannot be determined
from the hadronic momentum spectra. We additionally find that almost always a
sizeable transverse flow deve- lops, which causes the system to freeze out,
thereby limiting the flow velocity in itself. This freeze-out dominance in turn
makes a distinction between a plasma and a hadron resonance gas equation of
state very difficult, whereas a pure pion gas can easily be ruled out from
present data. To complete the picture we also analyze particle multiplicity
data, which suggest that chemical equilibrium is not reached with respect to
the strange particles. However, the over- population of pions seems to be at
most moderate, with a pion chemical potential far away from the Bose
divergence.Comment: 19 pages, 11 figs in separate uuencoded file, for LateX, epsf.tex,
dvips, TPR-94-5 and BNL-(no number yet
Strangeness Conservation in Hot Nuclear Fireballs
A constraint between thermal fireball parameters arises from the requirement
that the balance of strangeness in a fireball is (nearly) zero. We study the
impact of this constraint on (multi-)strange (anti-)baryon multiplicities and
compare the hadron gas and quark-gluon plasma predictions. We explore the
relation between the entropy content and particle multiplicities and show that
the data are compatible with the quark-gluon plasma hypothesis, but appear to
be inconsistent with the picture of an equilibrated hadron gas fireball. We
consider the implications of the results on the dynamics of evolution and decay
of the particle source.Comment: 35 pages, 11 postscript figures, report PAR/LPTHE/92--2
Thermal phenomenology of hadrons from 200 AGeV S+S collisions
We develop a complete and consistent description for the hadron spectra from
heavy ion collisions in terms of a few collective variables, in particular
temperature, longitudinal and transverse flow. To achieve a meaningful
comparison with presently available data, we also include the resonance decays
into our picture. To disentangle the influences of transverse flow and
resonance decays in the -spectra, we analyse in detail the shape of the
-spectra.Comment: 31 pages, 13 figs in seperate uuencoded file, for LaTeX, epsf.sty and
dvips, TPR-93-16 and BNL-(no number yet
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