17 research outputs found
Characteristics of Parton Energy Loss Studied with High-p_T Particle Spectra from PHENIX
In the first three years of the physics program at the Relativistic Heavy Ion
Collider (RHIC) a picture was established in which the suppression of hadrons
at high transverse momenta (p_T) in central Au+Au collisions is explained by
energy loss of quark and gluon jets in a medium of high color-charge density.
Measurements of single particle spectra for a smaller nucleus (Cu), for
different center-of-mass energies and with higher statistics were performed in
the subsequent years and are used to test predictions and assumptions of jet
quenching models in more detail. The measurements presented here are consistent
with a parton energy loss scenario so that these models can be used to relate
the observed suppression to properties of the created medium.Comment: To appear in the proceedings of 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008),
Jaipur, India, 04-10 Feb 200
Interferometry of direct photons in Pb+Pb collisions at 158 AGeV
We present final results from the WA98 experiment which provide first
measurements of Bose-Einstein correlations of direct photons in
ultrarelativistic heavy ion collisions. Invariant interferometric radii were
extracted in the range MeV/c and compared to interferometric
radii of charged pions. The yield of direct photons for MeV/c was
extracted from the correlation strength parameter and compared to the yield of
direct photons measured in WA98 at higher with the statistical
subtraction method, and to predictions of a fireball model.Comment: 4 pages, 3 figures, proceedings for Quark Matter 200
Event anisotropy in 4.2A GeV/c C+C collisions
The directed and elliptic flow of protons and negative pions in 4.2A GeV/c
C+C collisions is studied using the Fourier analysis of azimuthal
distributions. It is found that the protons exhibit pronounced directed flow,
while the flow of pions is either non existent or too weak to be detected
experimentally. Also, it is found that in the entire rapidity interval the
elliptic flow is very small if not zero. These results are confirmed by the
Quark-Gluon-String Model (QGSM) and the relativistic transport model (ART 1.0),
except that these models predict very weak antiflow of pions. The more detailed
comparison with the QGSM suggests that the decay of resonances and rescattering
of secondaries dominantly determine the proton and negative pion flow at this
energy.Comment: 7 pages, 3 figures, TeX file changed from double to single-spacin
Does HBT Measure the Freeze-out Source Distribution?
It is generally assumed that as a result of multiple scattering, the source
distribution measured in HBT interferometry corresponds to a chaotic source at
freeze-out. This assumption is subject to question as effects of multiple
scattering in HBT measurements must be investigated within a quantum-mechanical
framework. Applying the Glauber multiple scattering theory at high energies and
the optical model at lower energies, we find that multiple scattering leads to
an effective HBT density distribution that depends on the initial chaotic
source distribution with an absorption.Comment: 4 pages, talk presented at QM2004 Conference, January 11-17, 2004,
Oakland, California, USA, to be published in the Proceeding
Hard spectra and QCD matter: experimental review
The most significant experimental results on hadron spectra at large
transverse momentum available at the time of Quark Matter 2004 conference are
reviewed. Emphasis is put on those measurements that provide insights on the
properties of the QCD media, ``Quark Gluon Plasma'' and ``Color Glass
Condensate'', expected to be present in nucleus-nucleus collisions at collider
energies.Comment: 2 plots updated. Minor changes in tex
Electromagnetic Emission and Energy Loss in the QGP
I discuss why photon production from the Quark Gluon Plasma (QGP) presents an
interesting problem, both experimentally and theoretically. I show how the
photon emission rate can be computed under the simplifying assumption that the
QGP fully thermalizes. The theoretical issues are very similar to those for jet
energy loss; so it should be possible to treat them in a common formalism and
relate the predictions of one phenomenon to those of the other.Comment: 8 pages, invited talk at Quark Matter 200