224 research outputs found
Laying the groundwork at the AGS: Recent results from experiment E895
The E895 Collaboration at the Brookhaven AGS has performed a systematic
investigation of Au+Au collisions at 2-8 AGeV, using a large-acceptance Time
Projection Chamber. In addition to extensive measurements of particle flow,
spectra, two-particle interferometry, and strangeness production, we have
performed novel hybrid analyses, including azimuthally-sensitive pion HBT,
extraction of the six-dimensional pion phasespace density, and a first
measurement of the Lambda-proton correlation function.Comment: Presented at Quark Matter 2001, 8 pages, 5 figure
Near-threshold production of the multi-strange hyperon
The yield for the multi-strange hyperon has been measured in 6 AGeV
Au+Au collisions via reconstruction of its decay products and
, the latter also being reconstructed from its daughter tracks of
and p. The measurement is rather close to the threshold for
production and therefore provides an important test of model predictions. The
measured yield for and are compared for several
centralities. In central collisions the yield is found to be in
excellent agreement with statistical and transport model predictions,
suggesting that multi-strange hadron production approaches chemical equilibrium
in high baryon density nuclear matter.Comment: Submitted to PR
Comparison of Source Images for protons, 's and 's in 6 AGeV Au+Au collisions
Source images are extracted from two-particle correlations constructed from
strange and non-strange hadrons produced in 6 AGeV Au + Au collisions. Very
different source images result from pp vs p vs
correlations. These observations suggest important differences in the
space-time emission histories for protons, pions and neutral strange baryons
produced in the same events
Longitudinal Flow of Protons from 2-8 AGeV Central Au+Au Collisions
Rapidity distributions of protons from central Au + Au
collisions measured by the E895 Collaboration in the energy range from 2 to 8
AGeV at the Brookhaven AGS are presented. Longitudinal flow parameters derived
using a thermal model including collective longitudinal expansion are extracted
from these distributions. The results show an approximately linear increase in
the longitudinal flow velocity, , as a function of the
logarithm of beam energy.Comment: 5 Pages, including 3 figures, 1 tabl
Charged Pion Production in 2 to 8 AGeV Central Au+Au Collisions
Momentum spectra of charged pions over nearly full rapidity coverage from
target to beam rapidity have been measured in the 0-5% most central Au+Au
collisions in the beam energy range from 2 to 8 AGeV by the E895 Experiment.
Using a thermal parameterization to fit the transverse mass spectra, rapidity
density distributions are extracted. The observed spectra are compared with
predictions from the RQMD v2.3 cascade model and also to a thermal model
including longitudinal flow. The total 4 yields of the charged pions are
used to infer an initial state entropy produced in the collisions.Comment: 13 pgs, 19 figs, accepted by Phys. Rev. C. Data tables available at
http://nuclear.ucdavis.edu/~e895/published_spectra.htm
Model-independent source imaging using two-pion correlations in 2 to 8A GeV Au + Au collisions
We report a particle source imaging analysis based on two-pion correlations
in high multiplicity Au + Au collisions at beam energies between 2 and 8A GeV.
We apply the imaging technique introduced by Brown and Danielewicz, which
allows a model-independent extraction of source functions with useful accuracy
out to relative pion separations of about 20 fm. The extracted source functions
have Gaussian shapes. Values of source functions at zero separation are almost
constant across the energy range under study. Imaging results are found to be
consistent with conventional source parameters obtained from a multidimensional
HBT analysis.Comment: 4 pages, 3 figure
Azimuthally sensitive Hanbury Brown-Twiss interferometry in Au+Au collisions at sqrt(s_{NN}) = 200 GeV
We present the results of a systematic study of the shape of the pion
distribution in coordinate space at freeze-out in Au+Au collisions at RHIC
using two-pion Hanbury Brown-Twiss (HBT) interferometry. Oscillations of the
extracted HBT radii vs. emission angle indicate sources elongated perpendicular
to the reaction plane. The results indicate that the pressure and expansion
time of the collision system are not sufficient to completely quench its
initial shape.Comment: 6 pages, 4 figures, published versio
Rapidity and centrality dependence of proton and antiproton production from 197Au + 197Au collisions at √SNN = 130 GeV
We report on the rapidity and centrality dependence of proton and antiproton transverse mass distributions from 197Au + 197Au collisions at sqrt[sNN ]=130 GeV as measured by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). Our results are from the rapidity and transverse momentum range of |y| <0.5 and 0.35< pt <1.00 GeV/c . For both protons and antiprotons, transverse mass distributions become more convex from peripheral to central collisions demonstrating characteristics of collective expansion. The measured rapidity distributions and the mean transverse momenta versus rapidity are flat within |y| <0.5 . Comparisons of our data with results from model calculations indicate that in order to obtain a consistent picture of the proton (antiproton) yields and transverse mass distributions the possibility of prehadronic collective expansion may have to be taken into account
Production of Pairs Accompanied by Nuclear Dissociation in Ultra-Peripheral Heavy Ion Collision
We present the first data on pair production accompanied by nuclear
breakup in ultra-peripheral gold-gold collisions at a center of mass energy of
200 GeV per nucleon pair. The nuclear breakup requirement selects events at
small impact parameters, where higher-order corrections to the pair production
cross section should be enhanced. We compare the pair kinematic distributions
with two calculations: one based on the equivalent photon approximation, and
the other using lowest-order quantum electrodynamics (QED); the latter includes
the photon virtuality. The cross section, pair mass, rapidity and angular
distributions are in good agreement with both calculations. The pair transverse
momentum, , spectrum agrees with the QED calculation, but not with the
equivalent photon approach. We set limits on higher-order contributions to the
cross section. The and spectra are similar, with no evidence
for interference effects due to higher-order diagrams.Comment: 6 pages with 3 figures Slightly modified version that will appear in
Phys. Rev.
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