1,166 research outputs found
Hadron widths in mixed-phase matter
We derive classically an expression for a hadron width in a two-phase region
of hadron gas and quark-gluon plasma (QGP). The presence of QGP gives hadrons
larger widths than they would have in a pure hadron gas. We find that the
width observed in a central Au+Au collision at
GeV/nucleon is a few MeV greater than the width in a pure hadron gas. The part
of observed hadron widths due to QGP is approximately proportional to
.Comment: 8 pages, latex, no figures, KSUCNR-002-9
Field desorption ion source development for neutron generators
A new approach to deuterium ion sources for deuterium-tritium neutron
generators is being developed. The source is based upon the field desorption of
deuterium from the surfaces of metal tips. Field desorption studies of
microfabricated field emitter tip arrays have been conducted for the first
time. Maximum fields of 30 V/nm have been applied to the array tip surfaces to
date, although achieving fields of 20 V/nm to possibly 25 V/nm is more typical.
Both the desorption of atomic deuterium ions and the gas phase field ionization
of molecular deuterium has been observed at fields of roughly 20 V/nm and 20-30
V/nm, respectively, at room temperature. The desorption of common surface
adsorbates, such as hydrogen, carbon, water, and carbon monoxide is observed at
fields exceeding ~10 V/nm. In vacuo heating of the arrays to temperatures of
the order of 800 C can be effective in removing many of the surface
contaminants observed
Enhancement of low-mass dileptons in heavy-ion collisions
Using a relativistic transport model for the expansion stage of S+Au
collisions at 200 GeV/nucleon, we show that the recently observed enhancement
of low-mass dileptons by the CERES collaboration can be explained by the
decrease of vector meson masses in hot and dense hadronic matter.Comment: 12 pages, RevTeX, 3 figures available from [email protected]
Computing domains of attraction for planar dynamics
In this note we investigate the problem of computing the
domain of attraction of a
ow on R2 for a given attractor. We consider
an operator that takes two inputs, the description of the
ow and a cover
of the attractors, and outputs the domain of attraction for the given
attractor. We show that: (i) if we consider only (structurally) stable
systems, the operator is (strictly semi-)computable; (ii) if we allow all
systems de ned by C1-functions, the operator is not (semi-)computable.
We also address the problem of computing limit cycles on these systems
J/\psi production through resolved photon processes at e+ e- colliders
We consider J/psi photoproduction in e+ e- as well as linear photon
colliders. We find that the process is dominated by the resolved photon
channel. Both the once-resolved and twice-resolved cross-sections are sensitive
to (different combinations of) the colour octet matrix elements. Hence, this
may be a good testing ground for colour octet contributions in NRQCD. On the
other hand, the once-resolved J/psi production cross-section, particularly in a
linear photon collider, is sensitive to the gluon content of the photon. Hence
these cross-sections can be used to determine the parton distribution
functions, especially the gluon distribution, in a photon, if the colour octet
matrix elements are known.Comment: Added a figure on parametrisation dependence of photonic parton
densities and some reference
Formation of superdense hadronic matter in high energy heavy-ion collisions
We present the detail of a newly developed relativistic transport model (ART
1.0) for high energy heavy-ion collisions. Using this model, we first study the
general collision dynamics between heavy ions at the AGS energies. We then show
that in central collisions there exists a large volume of sufficiently
long-lived superdense hadronic matter whose local baryon and energy densities
exceed the critical densities for the hadronic matter to quark-gluon plasma
transition. The size and lifetime of this matter are found to depend strongly
on the equation of state. We also investigate the degree and time scale of
thermalization as well as the radial flow during the expansion of the
superdense hadronic matter. The flow velocity profile and the temperature of
the hadronic matter at freeze-out are extracted. The transverse momentum and
rapidity distributions of protons, pions and kaons calculated with and without
the mean field are compared with each other and also with the preliminary data
from the E866/E802 collaboration to search for experimental observables that
are sensitive to the equation of state. It is found that these inclusive,
single particle observables depend weakly on the equation of state. The
difference between results obtained with and without the nuclear mean field is
only about 20\%. The baryon transverse collective flow in the reaction plane is
also analyzed. It is shown that both the flow parameter and the strength of the
``bounce-off'' effect are very sensitive to the equation of state. In
particular, a soft equation of state with a compressibility of 200 MeV results
in an increase of the flow parameter by a factor of 2.5 compared to the cascade
case without the mean field. This large effect makes it possible to distinguish
the predictions from different theoretical models and to detect the signaturesComment: 55 pages, latex, + 39 figures available upon reques
Photoproduction in Scattering
We investigate the + c + photoproduction in
collision at the LEP II energy. The physical motivations for this study are: 1)
such next-to-leading order(NLO) process was not considered in previous
investigations of photoproduction in interaction, and it is
worthwhile to do so in order to make sound predictions for experimental
comparison; 2) from recent Belle experiment results, the process with same
final states at the factory has a theoretically yet unexplainable large
fraction; hence it is interesting to see what may happen at other colliders; 3)
the existing LEP data are marginal in observing such process, and at the planed
Linear Colliders(LCs) this process can be measured with high accuracy; 4) it is
necessary to take this process into consideration in the aim of elucidating the
quarkonium production mechanism, especially in testing the universality of
NRQCD nonperturbative matrix elements via photoproduction in
electron-position collisions.Comment: 15 pages, 3 figure
K^+ production in the reaction at incident energies from 1 to 2 AGeV
Semi-inclusive triple differential multiplicity distributions of positively
charged kaons have been measured over a wide range in rapidity and transverse
mass for central collisions of Ni with Ni nuclei. The transverse
mass () spectra have been studied as a function of rapidity at a beam
energy 1.93 AGeV. The distributions of K^+ mesons are well described by a
single Boltzmann-type function. The spectral slopes are similar to that of the
protons indicating that rescattering plays a significant role in the
propagation of the kaon. Multiplicity densities have been obtained as a
function of rapidity by extrapolating the Boltzmann-type fits to the measured
distributions over the remaining phase space. The total K^+ meson yield has
been determined at beam energies of 1.06, 1.45, and 1.93 AGeV, and is presented
in comparison to existing data. The low total yield indicates that the K^+
meson can not be explained within a hadro-chemical equilibrium scenario,
therefore indicating that the yield does remain sensitive to effects related to
its production processes such as the equation of state of nuclear matter and/or
modifications to the K^+ dispersion relation.Comment: 24 pages Latex (elsart) 7 PS figures to be submitted to Nucl. Phys
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
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