745 research outputs found
Kaon Phase Space Density in Heavy Ion Collisions
The first measurement of kaon phase space densities are presented as a
function of transverse mass, center of mass energy and the number of
participants. The kaon phase space density increases with the number of
participants from e+e- to Pb+Pb collisions. However the ratio of the kaon and
pion phase space densities at low transverse momentum is independent of the
number of participants for sqrt{s}=17GeV/nucleon
This paper is dedicated to Francis Riccardelli, engineer for the Port
Authority, who died on September 11th 2001 while evacuating others.Comment: 4 pages, 2 eps figures, proceedings of Strange Quarks in Matter,
Frankfurt 2001, submitted to J. Phys. G In response to referees comments I
derived an expresion for the ratio of kaon and pion phase space densites and
made several clarifications in the tex
Evaluation of Data Acquisition tools based on Java
One of the requirements of today's Data Acquisition systems is aMonitoring and Run Control tool which is easy to use, robust, easy tointegrate with the global environment and possibly portable onmultiple platforms. The ALICE DAQ group at CERN decided to evaluatethe possible use of WWW and Java for development in a quasi-on-linedistributed environment. An Event Display utility that was alreadyimplemented in C and Tcl/Tk was chosen as a test case and wastransposed in Java. We will describe the targets of the project, its evolution and the achieved results
Observing Non-Gaussian Sources in Heavy-Ion Reactions
We examine the possibility of extracting non-Gaussian sources from
two-particle correlations in heavy-ion reactions. Non-Gaussian sources have
been predicted in a variety of model calculations and may have been seen in
various like-meson pair correlations. As a tool for this investigation, we have
developed an improved imaging method that relies on a Basis spline expansion of
the source functions with an improved implementation of constraints. We examine
under what conditions this improved method can distinguish between Gaussian and
non-Gaussian sources. Finally, we investigate pion, kaon, and proton sources
from the p-Pb reaction at 450 GeV/nucleon and from the S-Pb reaction at 200
GeV/nucleon studied by the NA44 experiment. Both the pion and kaon sources from
the S-Pb correlations seem to exhibit a Gaussian core with an extended,
non-Gaussian halo. We also find evidence for a scaling of the source widths
with particle mass in the sources from the p-Pb reaction.Comment: 16 pages, 15 figures, 5 tables, uses RevTex3.
Interferometry with Resonances and Flow in High-Energy Nuclear Collisions
The effects of resonances and flow on the correlation function for two
identical particles are described assuming chaotic sources and classical
propagation of particles. Expanding to second order in relative momenta, the
source sizes can be calculated directly and understood as contributions from
various fluctuations in the source. Specific calculations of source size radii
are given assuming Bjorken longitudinal flow with additional transverse
expansion. Results are compared to recent and correlation data
from relativistic nuclear collisions with particular attention to the reduction
in the correlation function due to resonances and the decreasing
source sizes with increasing transverse momenta of the particles.Comment: 8 pages including 2 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
Two-Proton Correlations near Midrapidity in p+Pb and S+Pb Collisions at the CERN SPS
Correlations of two protons emitted near midrapidity in p+Pb collisions at
450 GeV/c and S+Pb collisions at 200A GeV/c are presented, as measured by the
NA44 Experiment. The correlation effect, which arises as a result of final
state interactions and Fermi-Dirac statistics, is related to the space-time
characteristics of proton emission. The measured source sizes are smaller than
the size of the target lead nucleus but larger than the sizes of the
projectiles. A dependence on the collision centrality is observed; the source
size increases with decreasing impact parameter. Proton source sizes near
midrapidity appear to be smaller than those of pions in the same interactions.
Quantitative agreement with the results of RQMD (v1.08) simulations is found
for p+Pb collisions. For S+Pb collisions the measured correlation effect is
somewhat weaker than that predicted by the model simulations, implying either a
larger source size or larger contribution of protons from long-lived particle
decays.Comment: 10 pages (LaTeX) text, 4 (EPS) figures; accepted for publication in
Phys. Lett.
Source Dimensions in Ultrarelativistic Heavy Ion Collisions
Recent experiments on pion correlations, interpreted as interferometric
measurements of the collision zone, are compared with models that distinguish a
prehadronic phase and a hadronic phase. The models include prehadronic
longitudinal expansion, conversion to hadrons in local kinetic equilibrium, and
rescattering of the produced hadrons. We find that the longitudinal and outward
radii are surprisingly sensitive to the algorithm used for two-body collisions.
The longitudinal radius measured in collisions of 200 GeV/u sulfur nuclei on a
heavy target requires the existence of a prehadronic phase which converts to
the hadronic phase at densities around 0.8-1.0 GeV/fm. The transverse radii
cannot be reproduced without introducing more complex dynamics into the
transverse expansion.Comment: RevTeX 3.0, 28 pages, 6 figures, not included, revised version, major
change is an additional discussion of the classical two-body collision
algorithm, a (compressed) postscript file of the complete paper including
figures can be obtained from Authors or via anonymous ftp at
ftp://ftp_int.phys.washington.edu/pub/herrmann/pisource.ps.
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