693 research outputs found
Improved Coulomb Correction Formulae for Bose-Einstein Correlations
We present improved Coulomb correction formulae for Bose-Einstein
correlations including also exchange term and use them to calculate appropriate
correction factors for several source functions. It is found that Coulomb
correction to the exchange function in the Bose-Einstein correlations cannot be
neglected.Comment: LaTex file, 8 pages, hard copies of 6 (multiple) figures available on
request to [email protected] or [email protected]
Charged seven-dimensional spacetimes with spherically symmetric extra-dimensions
We derive exact solutions of the seven-dimensional Einstein-Maxwell equations
for a spacetime exhibiting Poincare invariance along four-dimensions and
spherical symmetry in the extra-dimensions. Such topology generically arises in
the context of braneworld models. Our solutions generalise previous results on
Ricci-flat spacetimes admitting the two-sphere and are shown to include
wormhole configurations. A regular coordinate system suitable to describe the
whole spacetime is singled-out and we discuss the physical relevance of the
derived solutions.Comment: 14 pages, 8 figures, uses RevTeX. Physical discussion clarified,
wormhole solutions added. References adde
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.
Improving the sensitivity of future GW observatories in the 1-10 Hz band: Newtonian and seismic noise
The next generation gravitational wave interferometric detectors will likely be underground detectors to extend the GW detection frequency band to frequencies below the Newtonian noise limit. Newtonian noise originates from the continuous motion of the Earthâs crust driven by human activity, tidal stresses and seismic motion, and from mass density fluctuations in the atmosphere. It is calculated that on Earthâs surface, on a typical day, it will exceed the expected GW signals at frequencies below 10 Hz. The noise will decrease underground by an unknown amount. It is
important to investigate and to quantify this expected reduction and its effect on the sensitivity of future detectors, to plan for further improvement strategies. We report about some of these aspects. Analytical models can be used in the simplest scenarios to get a better qualitative and semi-quantitative understanding. As more complete modeling can be done numerically, we will discuss also some results obtained with a finite-element-based modeling tool. The method is verified by comparing its results with the results of analytic calculations for surface detectors. A key point about noise models is their initial parameters and conditions, which require detailed information about seismic motion in a real scenario. We will describe an effort to characterize the seismic activity at the Homestake mine which is currently in progress. This activity is specifically aimed to provide informations and to explore the site as a possible candidate for an underground observatory. Although the only compelling reason to put the interferometer underground is to reduce the Newtonian noise, we expect that the more stable underground environment will have a more general positive impact on the sensitivity.We will end this report with some considerations about seismic and suspension noise
Pion interferometry with pion-source-medium interactions
An extended pion source, which can be temporarily created by a high energy
nuclear collision, will also absorb and distort the outgoing pions. We discuss
how this effect alters the interferometric pattern of the two-pion momentum
correlation function. In particular, we show that the two-pion correlation
function decreases rapidly when the opening angle between the pions increases.
The opening-angle dependence should serve as a new means of obtaining
information about the pion source in the analysis of experimental data.Comment: 14 pages (revtex) and 9 figures (uuencoded), Caltech preprint
MAP-175, Indiana Univ. preprint IU/NTC 914-1
Coulomb corrections for Bose-Einstein correlations in whole momentum transfer region: Proposal of seamless fitting
We applied an improved Coulomb correction method developed by us recently to
data on identical KK-pairs production in S + Pb and p + Pb reactions at 200
GeV/c obtained by NA44 Collaboration. To analyse the whole range of the
momentum transfers measured the method of "seamless fitting" has been proposed
and used together with the asymptotic expansion formula for the Coulomb wave
function. We found that such Coulomb corrections lead sometimes to different
than previously reported (by NA44 Collaboration) interaction region and
strongly influence the long range correlations.Comment: LaTex file, 6 pages, hard copies of 5 figures available on request to
[email protected] or [email protected] (one new Fig. 5 added
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.
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.
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