280 research outputs found
New Results in the Analysis of the O+Si Elastic Scattering by Modifying the Optical Potential
The elastic scattering of the O+Si system has been analyzed
with a modified potential within the framework of the optical model over a wide
energy range in the laboratory system from 29.0 to 142.5 MeV. This system has
been extensively studied over the years and a number of serious problems has
remained unsolved: The explanation of the anomalous large angle scattering
data; the out-of-phase problem between theoretical predictions and experimental
data; the reproduction of the oscillatory structure near the Coulomb barrier;
the consistent description of angular distributions together with the
excitation functions data are just some of these problems. We propose the use
of a modified potential method to explain these problems over this wide energy
range. This new method consistently improves the agreement with the
experimental data and achieves a major improvement on all the previous Optical
model calculations for this system.Comment: 19 pages with 8 figure
Relative space-time asymmetries in pion and nucleon production in non-central nucleus-nucleus collisions at high energies
We propose to use the ratio of the pion-proton correlation functions
evaluated under different conditions to study the relative space-time
asymmetries in pion and proton emission (pion and nucleon source relative
shifts) in high energy heavy ion collision. We address the question of the
non-central collisions, where the sources can be shifted spatially both in the
longitudinal and in the transverse directions in the reaction plane. We use the
RQMD event generator to illustrate the effect and the technique.Comment: RevTex, 4 pages, 3 figures included as eps file
A Global Potential Analysis of the O+Si Reaction Using a New Type of Coupling Potential
A new approach has been used to explain the experimental data for the
O+Si system over a wide energy range in the laboratory system
from 29.0 to 142.5 MeV. A number of serious problems has continued to plague
the study of this system for a couple of decades. The explanation of anomalous
large angle scattering data; the reproduction of the oscillatory structure near
the Coulomb barrier; the out-of-phase problem between theoretical predictions
and experimental data; the consistent description of angular distributions
together with excitation functions data are just some of these problems. These
are long standing problems that have persisted over the years and do represent
a challenge calling for a consistent framework to resolve these difficulties
within a unified approach. Traditional frameworks have failed to describe these
phenomena within a single model and have so far only offered different
approaches where these difficulties are investigated separately from one
another. The present work offers a plausible framework where all these
difficulties are investigated and answered. Not only it improves the
simultaneous fits to the data of these diverse observables, achieving this
within a unified approach over a wide energy range, but it departs for its
coupling potential from the standard formulation. This new feature is shown to
improve consistently the agreement with the experimental data and has made
major improvement on all the previous coupled-channels calculations for this
system.Comment: 21 pages with 12 figure
Two-Proton Correlations from 14.6A GeV/c Si+Pb and 11.5A GeV/c Au+Au Central Collisions
Two-proton correlation functions have been measured in Si+Pb collisions at
14.6A GeV/c and Au+Au collisions at 11.5A GeV/c by the E814/E877 collaboration.
Data are compared with predictions of the transport model RQMD and the source
size is inferred from this comparison. Our analysis shows that, for both
reactions, the characteristic size of the system at freeze-out exceeds the size
of the projectile, suggesting that the fireball created in the collision has
expanded. For Au+Au reactions, the observed centrality dependence of the
two-proton correlation function implies that more central collisions lead to a
larger source sizes.Comment: RevTex, 12 pages, 5 figure
(Anti)Proton and Pion Source Sizes and Phase Space Densities in Heavy Ion Collisions
NA44 has measured mid-rapidity deuteron spectra from AA collisions at
sqrt{s}=18GeV/A at the CERN SPS. Combining these spectra with published proton,
antiproton and antideuteron data allows us to calculate, within a coalescence
framework, proton and antiproton source sizes and phase space densities. These
results are compared to pion source sizes and densities, pA results and to
lower energy (AGS) data. The antiproton source is larger than the proton source
at sqrt{s}=18GeV/A. The phase space densities of pions and protons are not
constant but grow with system size. Both pi+ and proton radii decrease with
transverse mass and increase with sqrt{s}. Pions and protons do not freeze-out
independently. The nature of their interaction changes as sqrt{s}, and the
pion/proton ratio increases.Comment: 4 pages, Latex 2.09, 3 eps figures. Changes for January 2001. The
proton source size is now calculated assuming a more realistic Hulthen,
rather than Gaussian, wavefunction. A new figure shows the effect of this
change which is important for small radii. A second new figure shows the
results of RQMD calculations of the proton source size and phase density.
Because of correlations between position and momentum coalesence does not
show the full proton source size. The paper has been streamlined and
readability improve
Elliptical flow -- a signature for early pressure in ultrarelativistic nucleus-nucleus collisions
Elliptical energy flow patterns in non-central Au(11.7AGeV) on Au reactions
have been studied employing the RQMD model. The strength of these azimuthal
asymmetries is calculated comparing the results in two different modes of RQMD
(mean field and cascade). It is found that the elliptical flow which is readily
observable with current experimental detectors may help to distinguish
different reasonable expansion scenarios for baryon-dense matter. The final
asymmetries are very sensitive to the pressure at maximum compression, because
they involve a partial cancelation between early squeeze-out and subsequent
flow in the reaction plane. This cancelation can be expected to occur in a
broad energy region covered by the current heavy ion fixed-target programs at
BNL and at CERN.Comment: 14 pages LaTeX including 3 postscript figure
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
Cold Strangelets Formation with Finite Size Effects in High Energy Heavy-Ion Collisions
We have studied the phase diagram and evolution of a strangelet in
equilibrium with a finite hadronic gas. Significant finite size modifications
of the phase diagram are found and their parameter dependences are studied.
With the inclusion of finite size effects we have also been able to obtain the
detailed properties of the cold strangelet emerging in the final stage of the
isentropic expansion of a finite strange fireball in high energy heavy-ion
collisions.Comment: 19 pages(RevTex), 11 Postscript figures; To appear in Phys. Rev.
Baryon Junction Loops in HIJING/B\=Bv2.0 and the Baryon/Meson Anomaly at RHIC
A new version, v2.0, of the HIJING/B\=B Monte Carlo nuclear collision event
generator is introduced in order to explore further the possible role of baryon
junctions loops in the baryon/meson anomaly (2 5 GeV/c) observed in
200A GeV Au+Au reactions at RHIC. We show that junction loops with an enhanced
intrinsic GeV/c transverse momentum kick may provide a partial
explanation of the anomaly as well as other important baryon stopping
observables.Comment: 27 pages, Latex(revtex), 8 figure
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