180 research outputs found
Rapidity and transverse momentum dependence of pion-pion Bose-Einstein correlations measured at 20, 30, 40, 80, and 158 AGeV beam energy
Preliminary results on pion-pion Bose-Einstein correlations in central Pb+Pb collisions measured by the NA49 experiment are presented. Rapidity as well as transverse momentum dependence of the HBT-radii are shown for collisions at 20, 30, 40, 80, and 158 AGeV beam energy. Including results from AGS and RHIC experiments only a weak energy dependence of the radii is observed. Based on hydrodynamical models parameters like lifetime and geometrical radius of the source are derived from the dependence of the radii on transverse momentum
Modification of jet-like correlations in Pb-Au at the SPS
A high statistics study of high- two-particle azimuthal correlations in
Pb-Au at GeV, performed by the CERES experiment at the
CERN-SPS, is presented. A broad away-side correlation with significant dip at
is observed. The shape and magnitude of the correlation
is similar to measurements at RHIC. In comparison to PYTHIA calculations, we
observe a significant excess of soft particles at the away-side. A study of
charge correlations between trigger and associated particles disfavors vacuum
fragmentation of the away-side jet and suggests significant energy transfer of
the hard-scattered parton to the medium.Comment: Proceedings to Quark Matter 2009 Conference, Knoxville, Tennessee,
US
Two- and three-particle azimuthal correlations of high-pt charged hadrons in Pb-Au collisions at 158A GeV/c
Azimuthal correlations of hadrons with high transverse momenta serve as a
measure to study the energy loss and the fragmentation pattern of jets emerging
from hard parton-parton interactions in heavy ion collisions. Preliminary
results from the CERES experiment on two- and three-particle correlations in
central Pb-Au collisions are presented. A strongly non-Gaussian shape on the
away-side of the two-particle correlation function is observed, indicating
significant interactions of the emerging partons with the medium. Mechanisms
like deflection of the initial partons or the evolution of a mach cone in the
medium can lead to similar modifications of the jet structure on the away-side.
An analysis based on three-particle correlations is presented which helps to
shed light on the origin of the observed away-side pattern.Comment: 4 pages, 2 figures, contribution to the Quark Matter conference 200
Energy Dependence of ÏâÏâBose-Einstein-Correlations in Central Heavy Ion Collisions measured by the Experiment NA49)
Um Signaturen fĂŒr die Erzeugung eines Quark-Gluon Plasmas zu untersuchen, wurden im Rahmen eines Energie-Scan Programmes mit dem Experiment NA49 am CERN-SPS Beschleunigerring bei 5 unterschiedlichen Strahlenergien Schwerionenkollisionen untersucht. Eine Möglichkeit, Informationen ĂŒber die raum-zeitliche Struktur einer solchen Kollision zu erhalten, ist durch die Untersuchung von Bose-Einstein-Korrelationen gegeben. Die Untersuchung der EnergieabhĂ€ngigkeit dieser Korrelationen ist Gegenstand dieser Arbeit. Um die Dynamik der Kollisionen zu studieren, wird die Analyse fĂŒr die einzelnen Energien in AbhĂ€ngigkeit des mittleren transversalen Impulses und der PaarrapiditĂ€t durchgefĂŒhrt. In der Arbeit werden zunĂ€chst die theoretischen Grundlagen zur Untersuchung von Schwerionenkollisionen mit Hilfe von Bose-Einstein-Korrelationen erarbeitet. Nach einer kurzen Darstellung des Experimentes NA49 folgt eine detaillierte Beschreibung der Datenselektion und der verwendeten Analyse-Methode. Die Ergebnisse werden im Rahmen eines Modells zur Beschreibung einer Teilchenquelle interpretiert
Transport model analysis of the transverse momentum and rapidity dependence of pion interferometry at SPS energies
Based on the UrQMD transport model, the transverse momentum and the rapidity
dependence of the Hanbury-Brown-Twiss (HBT) radii , , as well
as the cross term at SPS energies are investigated and compared with
the experimental NA49 and CERES data. The rapidity dependence of the ,
, is weak while the is significantly increased at large
rapidities and small transverse momenta. The HBT "life-time" issue (the
phenomenon that the calculated value is larger than
the correspondingly extracted experimental data) is also present at SPS
energies.Comment: 17 pages, 11 figure
Interferometry search for new forms of matter in A+A collisions
A method allowing studies of the hadronic matter at the early evolution stage
in A+A collisions is developed. It is based on an interferometry analysis of
approximately conserved values such as the averaged phase-space density (APSD)
and the specific entropy of thermal pions. The plateau found in the APSD
behavior vs collision energy at SPS is associated, apparently, with the
deconfinement phase transition at low SPS energies; a saturation of this
quantity at the RHIC energies indicates the limiting Hagedorn temperature for
hadronic matter.Comment: 4 pages, 3 figures, contribution to the Quark Matter 2005
proceedings, minor change
System-size dependence of the pion freeze-out volume as a potential signature for the phase transition to a Quark Gluon Plasma
Hanburry-Brown-Twiss (HBT) correlation functions and radii of negatively
charged pions from C+C, Si+Si, Cu+Cu, and In+In at lower RHIC/SPS energies are
calculated with the UrQMD transport model and the CRAB analyzing program. We
find a minimum in the excitation function of the pion freeze-out volume at low
transverse momenta and around GeV which can be related to
the transition from hadronic to string matter (which might be interpreted as a
pre-cursor of the QGP). The existence of the minimum is explained by the
competition of two mechanisms of the particle production, resonance decays and
string formation/fragmentation.Comment: 12 pages, 4 fig
Evidence for an exotic S=-2, Q=-2 baryon resonance in proton-proton collisions at the CERN SPS
Results of resonance searches in the Xi - pi -, Xi - pi +, Xi -bar+ pi -, and Xi -bar+ pi + invariant mass spectra in proton-proton collisions at sqrt[s]=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi - pi - baryon resonance with mass of 1.862±0.002 GeV/c2 and width below the detector resolution of about 0.018 GeV/c2. The significance is estimated to be above 4.2 sigma . This state is a candidate for the hypothetical exotic Xi --3/2 baryon with S=-2, I=3 / 2, and a quark content of (dsdsu-bar). At the same mass, a peak is observed in the Xi - pi + spectrum which is a candidate for the Xi 03/2 member of this isospin quartet with a quark content of (dsusd-bar). The corresponding antibaryon spectra also show enhancements at the same invariant mass
Quark Matter 2006: high-pT and jets
An overview of new experimental results on high-\pT{} particle production and
jets in heavy ion collisions from the Quark Matter 2006 conference is
presented.Comment: Presented at Quark Matter 200
The effect of "pre-formed" hadron potentials on the dynamics of heavy ion collisions and the HBT puzzle
The nuclear stopping, the elliptic flow, and the HBT interferometry are
calculated by the UrQMD transport model, in which potentials for "pre-formed"
particles (string fragments) from color fluxtube fragmentation as well as for
confined particles are considered. This description provides stronger pressure
at the early stage and describes these observables better than the default
cascade mode (where the "pre-formed" particles from string fragmentation are
treated to be free-streaming). It should be stressed that the inclusion of
potential interactions pushes down the calculated HBT radius and pulls up
the so that the HBT time-related puzzle disappears throughout the
energies from AGS, SPS, to RHIC.Comment: 6 pages, 4 figures. Accepted for publication in Phys. Lett.
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