743 research outputs found
Liquid-Gas Phase Transition in Nuclear Equation of State
A canonical ensemble model is used to describe a caloric curve of nuclear
liquid-gas phase transition. Allowing a discontinuity in the freeze out density
from one spinodal density to another for a given initial temperature, the
nuclear liquid-gas phase transition can be described as first order. Averaging
over various freeze out densities of all the possible initial temperatures for
a given total reaction energy, the first order characteristics of liquid-gas
phase transition is smeared out to a smooth transition. Two experiments, one at
low beam energy and one at high beam energy show different caloric behaviors
and are discussed.Comment: 12 pages in Revtex including two Postscript figure
Universal Behavior of Lyapunov Exponents in Unstable Systems
We calculate the Lyapunov exponents in a classical molecular dynamics
framework. The system is composed of few hundreds particles interacting either
through Yukawa (Nuclear) or Slater-Kirkwood (Atomic) forces. The forces are
chosen to give an Equation of State that resembles the nuclear and the atomic
Equation Of State respectively near the critical point for liquid-gas
phase transition. We find the largest fluctuations for an initial "critical
temperature". The largest Lyapunov exponents are always positive and
can be very well fitted near this "critical temperature" with a functional form
, where the exponent is
independent of the system and mass number. At smaller temperatures we find that
, a universal behavior characteristic of an order
to chaos transition.Comment: 11 pages, RevTeX, 3 figures not included available upon reques
Application of Information Theory in Nuclear Liquid Gas Phase Transition
Information entropy and Zipf's law in the field of information theory have
been used for studying the disassembly of nuclei in the framework of the
isospin dependent lattice gas model and molecular dynamical model. We found
that the information entropy in the event space is maximum at the phase
transition point and the mass of the cluster show exactly inversely to its
rank, i.e. Zipf's law appears. Both novel criteria are useful in searching the
nuclear liquid gas phase transition experimentally and theoretically.Comment: 5 pages, 5 figure
An investigation of standard thermodynamic quantities as determined via models of nuclear multifragmentation
Both simple and sophisticated models are frequently used in an attempt to
understand how real nuclei breakup when subjected to large excitation energies,
a process known as nuclear multifragmentation. Many of these models assume
equilibriumthermodynamics and produce results often interpreted as evidence of
a phase transition. This work examines one class of models and employs standard
thermodynamical procedure to explore the possible existence and nature of a
phase transition. The role of various terms, e.g. Coulomb and surface energy,
is discussed.Comment: 19 two-column format pages with 24 figure
Equation of State, Spectra and Composition of Hot and Dense Infinite Hadronic Matter in a Microscopic Transport Model
Equilibrium properties of infinite relativistic hadron matter are
investigated using the Ultrarelativistic Quantum Molecular Dynamics (UrQMD)
model. The simulations are performed in a box with periodic boundary
conditions. Equilibration times depend critically on energy and baryon
densities. Energy spectra of various hadronic species are shown to be isotropic
and consistent with a single temperature in equilibrium. The variation of
energy density versus temperature shows a Hagedorn-like behavior with a
limiting temperature of 13010 MeV. Comparison of abundances of different
particle species to ideal hadron gas model predictions show good agreement only
if detailed balance is implemented for all channels. At low energy densities,
high mass resonances are not relevant; however, their importance raises with
increasing energy density. The relevance of these different conceptual
frameworks for any interpretation of experimental data is questioned.Comment: Latex, 20 pages including 6 eps-figure
Statistical signatures of critical behavior in small systems
The cluster distributions of different systems are examined to search for
signatures of a continuous phase transition. In a system known to possess such
a phase transition, both sensitive and insensitive signatures are present;
while in systems known not to possess such a phase transition, only insensitive
signatures are present. It is shown that nuclear multifragmentation results in
cluster distributions belonging to the former category, suggesting that the
fragments are the result of a continuous phase transition.Comment: 31 pages, two columns with 30 figure
Event-by-Event Fluctuations in Heavy Ion Collisions and the QCD Critical Point
The event-by-event fluctuations of suitably chosen observables in heavy ion
collisions at SPS, RHIC and LHC can tell us about the thermodynamic properties
of the hadronic system at freeze-out. By studying these fluctuations as a
function of varying control parameters, it is possible to learn much about the
phase diagram of QCD. As a timely example, we stress the methods by which
present experiments at the CERN SPS can locate the second-order critical
endpoint of the first-order transition between quark-gluon plasma and hadron
matter. Those event-by-event signatures which are characteristic of freeze-out
in the vicinity of the critical point will exhibit nonmonotonic dependence on
control parameters. We focus on observables constructed from the multiplicity
and transverse momenta of charged pions. We first consider how the
event-by-event fluctuations of such observables are affected by Bose-Einstein
correlations, by resonances which decay after freeze-out and by fluctuations in
the transverse flow velocity. We compare our thermodynamic predictions for such
noncritical event-by-event fluctuations with NA49 data, finding broad
agreement. We then focus on effects due to thermal contact between the observed
pions and a heat bath with a given (possibly singular) specific heat, and due
to the direct coupling between the critical fluctuations of the sigma field and
the observed pions. We also discuss the effect of the pions produced in the
decay of sigma particles just above threshold after freeze-out on the inclusive
pion spectrum and on multiplicity fluctuations. We estimate the size of these
nonmonotonic effects which appear near the critical point, including
restrictions imposed by finite size and finite time, and conclude that they
should be easily observable.Comment: 58 pages, 2 figures; to appear in Phys. Rev.
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