30 research outputs found
Geometry, Scaling and Universality in the Mass Distributions in Heavy Ion Collisions
Various features of the mass yields in heavy ion collisions are studied. The
mass yields are discussed in terms of iterative one dimensional discrete maps.
These maps are shown to produce orbits for a monomer or for a nucleus which
generate the mass yields and the distribution of cluster sizes. Simple
Malthusian dynamics and non-linear Verhulst dynamics are used to illustrate the
approach. Nuclear cobwebbing, attractors of the dynamics, and Lyapanov
exponents are discussed for the mass distribution. The self-similar property of
the Malthusian orbit offers a new variable for the study of scale invariance
using power moments of the mass distribution. Correlation lengths, exponents
and dimensions associated with scaling relations are developed. Fourier
transforms of the mass distribution are used to obtain power spectra which are
investigated for a behavior.Comment: 29 pages in REVTEX, 9 figures (available from the authors), RU-92-0
Critical Exponents and Particle Multiplicity Distributions in High Energy Collisions
Data from the L3, Tasso, Opal and Delphi collaborations are analyzed in terms
of a statistical model of high energy collisions. The model contains a power
law critical exponent tau and Levy index alpha. These data are used to study
values of tau and alpha. The very high multiplicity events in L3, Opal and
Delphi are consistent with a model based on a Feynman-Wilson gas which has a
tail exponent tau=3/2 and alpha=1/2.Comment: 10 pages, new table adde
Critical point multiplicities and multiplicity fluctuations in heavy ion collisions
An exactly solvable model of nuclear fragmentation is shown to lead to a
simple connection between the critical point multiplicity and the critical point exponent recently reported on in the
EOS collaboration. The importance of multiplicity fluctuations on critical
point behavior is also discussed.Comment: 6 pages (revtex), 1 fig. avail. on request, submitted to Phys. Lett.
Development of particle multiplicity distributions using a general form of the grand canonical partition function and applications to L3 and H1 Data
Various phenomenological models of particle multiplicity distributions are
discussed using a general form of a unified model which is based on the grand
canonical partition function and Feynman's path integral approach to
statistical processes. These models can be written as special cases of a more
general distribution which has three control parameters which are , ,
. The relation to these parameters to various physical quantities are
discussed. A connection of the parameter with Fisher's critical exponent
is developed. Using this grand canonical approach, moments, cumulants
and combinants are discussed and a physical interpretation of the combinants
are given and their behavior connected to the critical exponent . Various
physical phenomena such as hierarchical structure, void scaling relations, KNO
scaling features, clan variables, and branching laws are shown in terms of this
general approach. Several of these features which were previously developed in
terms of the negative binomial distribution are found to be more general. Both
hierarchical structure and void scaling relations depend on the Fisher exponent
. Applications of our approach to the charged particle multiplicity
distribution in jets of L3 and H1 data are given. It is shown that just looking
at the mean and fluctuation of data is not enough to distinguish these
distributions or the underlying mechanism. The mean, fluctuation and third
cummulant of distribution determine three parameters , , . We find
that a generalized random work model fits the data better than the widely used
negative binomial model.Comment: 7 figures include
A Bose-Einstein Model of Particle Multiplicity Distributions
A model of particle production is developed based on a parallel with a theory
of Bose-Einstein condensation and similarities with other critical phenomena
such as critical opalescence. The role of a power law critical exponent tau and
Levy index alpha are studied. Various features of this model are developed and
compared with other commonly used models of particle production which are shown
to differ by having different values for tau, alpha. While void scaling is a
feature of this model, hierarchical structure is not a general property of it.
The value of the exponent tau=2 is a transition point associated with void and
hierarchical scaling features. An exponent gamma is introduced to describe
enhanced fluctuations near a critical point. Experimentally determined
properties of the void scaling function can be used to determine tau.Comment: Accepted for publication in Nucl. Phys.
Model of multifragmentation, Equation of State and phase transition
We consider a soluble model of multifragmentation which is similar in spirit
to many models which have been used to fit intermediate energy heavy ion
collision data. We draw a p-V diagram for the model and compare with a p-V
diagram obtained from a mean-field theory. We investigate the question of
chemical instability in the multifragmentation model. Phase transitions in the
model are discussed.Comment: Revtex, 9 pages including 6 figures: some change in the text and Fig.
Baryon phase-space density in heavy-ion collisions
The baryon phase-space density at mid-rapidity from central heavy-ion
collisions is estimated from proton spectra with interferometry and deuteron
coalescence measurements. It is found that the mid-rapidity phase-space density
of baryons is significantly lower at the SPS than the AGS, while those of total
particles (pion + baryon) are comparable. Thermal and chemical equilibrium
model calculations tend to over-estimate the phase-space densities at both
energies.Comment: 5 pages, 2 tables, no figure. RevTeX style. Accepted for publication
in Phys. Rev. C Rapid Communicatio
Widths of Isobaric Analog Resonances: a microscopic approach
A self-consistent particle-phonon coupling model is used to investigate the
properties of the isobaric analog resonance in Bi. It is shown that
quantitative agreement with experimental data for the energy and the width can
be obtained if the effects of isospin-breaking nuclear forces are included, in
addition to the Coulomb force effects. A connection between microscopic model
predictions and doorway state approaches which make use of the isovector
monopole resonance, is established via a phenomenological ansatz for the
optical potential.Comment: 18 pages, 1 figure. To appear on Phys. Rev. C (tentatively scheduled
for June 1998
Universal features of the order-parameter fluctuations : reversible and irreversible aggregation
We discuss the universal scaling laws of order parameter fluctuations in any
system in which the second-order critical behaviour can be identified. These
scaling laws can be derived rigorously for equilibrium systems when combined
with the finite-size scaling analysis. The relation between order parameter,
criticality and scaling law of fluctuations has been established and the
connexion between the scaling function and the critical exponents has been
found. We give examples in out-of-equilibrium aggregation models such as the
Smoluchowski kinetic equations, or of at-equilibrium Ising and percolation
models.Comment: 19 pages, 10 figure