168 research outputs found
The ``Out-Longitudinal'' Cross Term and Other Model Independent Features of the Two-Particle HBT Correlation Function
Using two specific models and a model independent formalism, we show that an
``out-longitudinal'' cross term should be included in any gaussian fits to
correlation data. In addition, we show that correlation radii (including the
cross term) measure lengths of homogeneity within the source, not necessarily
geometric sizes.Comment: 4 pages, uuencoded compressed postscrip
Lifetimes and Sizes from Two-Particle Correlation Functions
We discuss the Yano-Koonin-Podgoretskii (YKP) parametrization of the
two-particle correlation function for azimuthally symmetric expanding sources.
We derive model-independent expressions for the YKP fit parameters and discuss
their physical interpretation. We use them to evaluate the YKP fit parameters
and their momentum dependence for a simple model for the emission function and
propose new strategies for extracting the source lifetime. Longitudinal
expansion of the source can be seen directly in the rapidity dependence of the
Yano-Koonin velocity.Comment: 15 pages REVTEX, 2 figures included, submitted to Phys. Lett. B,
Expanded discussion of disadvantages of standard HBT fit and of Fig.
Universal Pion Freeze-out Phase-Space Density
Results on the pion freeze-out phase-space density in sulphur-nucleus, Pb-Pb
and pion-proton collisions at CERN-SPS are presented. All heavy-ion reactions
are consistent with the thermal Bose-Einstein distrtibution f=1/(exp(E/T)-1) at
T~120 MeV, modified for expansion. Pion-proton data are also consistent with f,
but at T~180 MeV.Comment: 1 page, 1 figure; 98' report for GSI-Darmstad
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.
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.
Bose-Einstein Correlations for Three-Dimensionally Expanding, Cylindrically Symmetric, Finite Systems
The parameters of the Bose-Einstein correlation function may obey an {\it
-scaling}, as observed in and reactions at CERN SPS.
This -scaling implies that the Bose-Einstein correlation functions view
only a small part of the big and expanding system. The full sizes of the
expanding system at the last interaction are shown to be measurable with the
help the invariant momentum distribution of the emitted particles. A vanishing
duration parameter can also be generated in the considered model-class with a
specific dependence.Comment: 35 pages, ReVTeX, LaTeX, no figures, discussion extende
(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
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
The full-length prototype of the KLOE drift chamber
The main goal of the KLOE experiment is the study of CP violation in the K mesons system, with an accuracy of 10(-4) in the measurement of Re(epsilon'/epsilon). This task imposes strong constraints on the design and operation of the drift chamber, which must reconstruct the charged decays of low momentum K-L's and K-S's with high efficiency and high resolution, full-length prototype of the chamber has been built and tested on a 50 GeV/c beam. The analysis of the large sample of data has allowed a detailed study of the time to distance relations as a function of the track parameters and of the peculiar geometry of the drift cell, The detector performance, in terms of efficiency, spatial resolutions and dE/dx resolution, is illustrated and discussed
- …