424 research outputs found
Jet Fragmentation in Vacuum and Medium with gamma-hadron Correlations in PHENIX
Jet fragmentation in p+p and Au+Au collisions is studied via back-to-back
correlations of direct photons and charged hadrons. The direct photon
correlations are obtained by statical subtraction of the background from decay
photons. Results on the nuclear modification to the associated charged hadron
yields are reviewed. Further studies of jet fragmentation in p+p using isolated
direct photons are also presented. A kT-smeared LO pQCD calculation is used to
interpret the data. The sensitivity of the data to the underlying fragmentation
function is tested and the results are found to be compatible with expectations
of a sample dominated by quark jet fragmentation.Comment: Talk presented at Hot Quarks 2010, June 21-26, La Londe Les Maures,
France. To be published in Journal of Physics: Conference Series (JPCS
Dynamics of Particle Production in Relativistic Nuclear Collisions
Saturation models for particle production in relativistic nuclear collisions
are discussed. In particular, I show that the predictions from the high density
QCD for the qualitative shape of are very sensitive to the form of the
unintegrated gluon distribution.Comment: 4 pages, 4 figures, Proceedings for Quark Matter 200
Stopping and Baryon Transport in Heavy Ion Reactions
In this report I will give an experimental overview on nuclear stopping in
hadron collisions, and relate observations to understanding of baryon
transport. Baryon number transport is not only evidenced via net-proton
distributions but also by the enhancement of strange baryons near mid-rapidity.
Although the focus is on high-energy data obtained from pp and heavy ions from
RHIC, relevant data from SPS and ISR will be considered. A discussion how the
available data at higher energy relates and gives information on baryon
junction, quark-diquark breaking will be made.Comment: 8 pages, 7 figures. Invited plenary talk for the 5'th international
conference on Physics and Astrophysics of Quark Gluon Plasma, February 8-12,
2005, Salt Lake City, Kolkata, Indi
Elliptic flow of the dilute Fermi gas: From kinetics to hydrodynamics
We use the Boltzmann equation in the relaxation time approximation to study
the expansion of a dilute Fermi gas at unitarity. We focus, in particular, on
the approach to the hydrodynamic limit. Our main finding are: i) In the regime
that has been studied experimentally hydrodynamic effects beyond the
Navier-Stokes approximation are small, ii) mean field corrections to the
Boltzmann equation are not important, iii) experimental data imply that
freezeout occurs very late, that means that the relaxation time remains smaller
than the expansion time during the entire evolution of the system, iv) the
experimental results also imply that the bulk viscosity is significantly
smaller than the shear viscosity of the system.Comment: 18 pages, 6 figure
Suppression of hadrons with large transverse momentum in central Au+Au collisions at √s<SUB>NN</SUB> = 130GeV
Transverse momentum spectra for charged hadrons and for neutral pions in the range 1GeV/c<pT<5GeV/c have been measured by the PHENIX experiment at RHIC in Au+Au collisions at √sNN = 130GeV. At high pT the spectra from peripheral nuclear collisions are consistent with scaling the spectra from p+p collisions by the average number of binary nucleon-nucleon collisions. The spectra from central collisions are significantly suppressed when compared to the binary-scaled p+p expectation, and also when compared to similarly binary-scaled peripheral collisions, indicating a novel nuclear-medium effect in central nuclear collisions at RHIC energies
Relativistic Heavy-Ion Physics: Experimental Overview
The field of relativistic heavy-ion physics is reviewed with emphasis on new
results and highlights from the first run of the Relativistic Heavy-Ion
Collider at BNL and the 15 year research programme at the SPS at CERN and the
AGS at BNL.Comment: 15 pages, 9 figures. Invited Talk at the Fourth International
Conference on Physics and Astrophysics of Quark Gluon Plasma, (ICPAQGP-2001)
Jaipur, India, November 26-30, 200
Study of Cronin effect and nuclear modification of strange particles in d-Au and Au-Au collisions at 200 GeV in PHENIX
Effects of strangeness on nuclear modification in d-Au and Au-Au collisions
at 200 GeV are studied, in order to quantify the effects of quark content and
mass. Measurements of ratios of the yields in central collisions to the yields
in peripheral collisions are performed for lambda baryon and phi meson. Found
results show little dependence of particle suppression or enhancement on mass
and strange content, but rather prominent difference in nuclear modification
between mesons and baryons.Comment: 4 pages, 4 figures, proceedings of the Seventeenth International
Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter
2004
Measurement of the Transverse Single Spin Asymmetry of + + at = 200 GeV
The measurement of transverse single spin asymmetries () provides
insight into the structure of the nucleon. Several mechanisms have been
proposed that attempt to explain based on QCD, and additional
measurements of for different processes further constrain these models.
Using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC), we
study transversely polarized p+p collisions. Results from PHENIX and other
experiments show significant asymmetries in the forward region, which could be
due to contributions from both the Sivers and the Collins effects. Studying the
species as well as the kinematic dependencies of these transverse single spin
asymmetries will help to disentangle the origin of the observed asymmetries.
Therefore, measurements of with inclusive mesons at forward
rapidities are an important tool for the understanding of these asymmetries. In
2008, the PHENIX experiment collected 5.2 pb integrated luminosity in
collisions at = 200 GeV. The status of the asymmetry
analysis of mesons at forward rapidity will be shown.Comment: 4 pages, 3 figure
Formation Time of QGP from Thermal Photon Elliptic Flow
We show that the transverse momentum dependent elliptic flow of
thermal photons is quite sensitive to the initial formation time () of
Quark Gluon Plasma (QGP) for semi-central collision of gold nuclei at RHIC
\cite{tau}. A smaller value of the formation time or a larger initial
temperature leads to a significant increase in the thermal photon radiation
from QGP phase, which has a smaller . The elliptic flow of thermal photon
is dominated by the contribution from the quark matter at intermediate and high
range and as a result sum decreases with smaller for GeV. On the other hand we find that the elliptic flow parameter for
hadrons depends only marginally on the value of .Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee, v2: minor
correction
Beam-Energy and System-Size Dependence of Dynamical Net Charge Fluctuations
We present measurements of net charge fluctuations in collisions at
19.6, 62.4, 130, and 200 GeV, collisions at
62.4, 200 GeV, and collisions at 200
GeV using the net charge dynamical fluctuations measure . The
dynamical fluctuations are non-zero at all energies and exhibit a rather modest
dependence on beam energy. We find that at a given energy and collision system,
net charge dynamical fluctuations violate scaling, but display
approximate scaling. We observe strong dependence of dynamical
fluctuations on the azimuthal angular range and pseudorapidity widths.Comment: 4 pages, 4 figures, presented at the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 200
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