986 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
Initial temperature and EoS of quark matter from direct photons
The time evolution of the quark gluon plasma created in gold-gold collisions
of the Relativistic Heavy Ion Collider (RHIC) can be described by
hydrodynamical models. Distribution of hadrons reflects the freeze-out state of
the matter. To investigate the time evolution one needs to analyze penetrating
probes, such as direct photon spectra. Distributions of low energy photons was
published in 2010 by PHENIX. In this paper we analyze a 3+1 dimensional
solution of relativistic hydrodynamics and calculate momentum distribution of
direct photons. Using earlier fits of this model to hadronic spectra, we
compare photon calculations to measurements and find that the initial
temperature of the center of the fireball is at least 519+-12 MeV, while for
the equation of state we get c_s= 0.36+-0.02.Comment: Talk at the VI Workshop on Particle Correlations and Femtoscopy,
Kiev, September 14-18, 2010. 6 pages, 1 figure. This work was supported by
the OTKA grant NK73143 and M. Csanad's Bolyai scholarshi
Heavy Quarkonia Production in p+p Collisions from the PHENIX Experiment
Quarkonia provide a sensitive probe of the properties of the hot dense medium
created in high energy heavy ion collisions. Hard scattering processes result
in the production of heavy quark pairs that interact with the collision medium
during hadronization. These in-medium interactions convey information about the
fundamental properties of the medium itself and can be used to examine the
modification of the QCD confining potential in the collision environment.
Baseline measurements from p+p and d+Au collision systems are used to
distinguish cold nuclear matter effects while measurements from heavy ion
collision systems are used to quantify in-medium effects. The PHENIX experiment
has the capability of detecting heavy quarkonia at via the
decay channel and at via the decay channel.
Recent runs have resulted in the collection of high statistics p+p data sets
that provide an essential baseline reference for heavy ion measurements and
allow for further critical evaluation of heavy quarkonia production mechanisms.
The latest PHENIX results for the production of the in p+p collisions
are presented and future prospects for , and
measurements are discussed.Comment: 4 pages, 2 figures, Proceedings for Quark Matter 200
Quarkonium production in ultra-relativistic nuclear collisions: suppression vs. enhancement
After a brief review of the various scenarios for quarkonium production in
ultra-relativistic nucleus-nucleus collisions we focus on the ingredients and
assumptions underlying the statistical hadronization model. We then confront
model predictions for J/ phase space distributions with the most recent
data from the RHIC accelerator. Analysis of the rapidity dependence of the
J/ nuclear modification factor yields first evidence for the production
of J/ mesons at the phase boundary. We conclude with predictions for
charmonium production at the LHC.Comment: 8 pages, 6 figures, invited paper, Quark Matter 2006 conference,
Shanghai, submitted to J. Phys.
Correlations of Electrons from Heavy Flavor Decay with Hadrons in Au+Au and p+p Collisions
Measurements of electrons from the decay of open-heavy flavor mesons have
shown that the yields are suppressed in Au+Au collisions compared to
expectations from binary-scaled p+p collisions. These measurements indicate
that charm and bottom quarks interact with the hot-dense matter produced in
heavy-ion collisions much more than expected. Here we extend these studies to
two-particle correlations where one particle is an electron from the decay of a
heavy-flavor meson and the other is a charged hadron from either the decay of
the heavy meson or from jet fragmentation. These measurements provide more
detailed information about the interactions between heavy quarks and the
matter, such as whether the modifcation of the away-side-jet shape seen in
hadron-hadron correlations is present when the trigger particle is from
heavy-meson decay and whether the overall level of away-side-jet suppression is
consistent. We statistically subtract correlations of electrons arising from
background sources from the inclusive electron-hadron correlations and obtain
two-particle azimuthal correlations at =200 GeV between
electrons from heavy-flavor decay with charged hadrons in p+p and also first
results in Au+Au collisions. We find the away-side-jet shape and yield to be
modified in Au+Au collisions compared to p+p collisions.Comment: talk given at Winter Workshop in Nuclear Dynamics 201
A method of eta' decay product selection to study partial chiral symmetry restoration
In case of chiral U_A(1) symmetry restoration the mass of the eta' boson (the
ninth, would-be Goldstone boson) is decreased, thus its production cross
section is heavily enhanced. The eta' decays (through one of its decay
channels) into five pions. These pions will not be correlated in terms of
Bose-Einsten correlations, thus the production enhancement changes the strength
of two-pion correlation functions at low momentum. Preliminary results strongly
support the mass decrease of the eta' boson. In this paper we propose a method
to select pions coming from eta' decays. We investigate the efficiency of the
proposed kinematical cut in several collision systems and energies with several
simulators. We prove that our method can be used in all investigeted collision
systems.Comment: Talk at the VI Workshop on Particle Correlations and Femtoscopy,
Kiev, September 14-18, 2010. 6 pages, 3 figures. This work was supported by
the OTKA grant NK73143 and M. Csanad's Bolyai scholarshi
Highlights from PHENIX - II
This contribution highlights recent results from the PHENIX Collaboration at
RHIC with emphasis on those obtained through lepton and photon measurements in
PHENIX.Comment: 9 pages, 13 figures, presented at the 20th International Conference
on Ultra-Relativistic Nucleus-Nucleus Collisions - "Quark Matter 2008",
Jaipur, India, February 4-10, 200
Hotter, Denser, Faster, Smaller...and Nearly-Perfect: What's the matter at RHIC?
The experimental and theoretical status of the ``near perfect fluid'' at RHIC
is discussed. While the hydrodynamic paradigm for understanding collisions at
RHIC is well-established, there remain many important open questions to address
in order to understand its relevance and scope. It is also a crucial issue to
understand how the early equilibration is achieved, requiring insight into the
active degrees of freedom at early times.Comment: 10 Pages, 13 Figures, submitted to the proceedings of the Second
Meeting of the APS Topical Group on Hadronic Physics, Nashville, TN, October
22-24, 200
Measurement of light mesons at RHIC by the PHENIX experiment
The PHENIX experiment at RHIC has measured a variety of light neutral mesons
(, K, , , , ) via
multi-particle decay channels over a wide range of transverse momentum. A
review of the recent results on the production rates of light mesons in p+p and
their nuclear modification factors in d+Au, Cu+Cu and Au+Au collisions at
different energies is presented.Comment: 5 pages, 4 figures, talk given at Hard Probes 2008 conference in La
Toja, Spain. submitted to EPJ
Photon-tagged jet measurements in Pb+Pb collisions with the CMS detector
Presented are the results of a detailed study for a complete simulation of
the CMS detectors at the LHC in view of the expected modification of jet
fragmentation functions in central Pb+Pb collisions at (s_NN)**0.5=5.5 TeV
compared to the vacuum (p+p) case. The study is based on photon-jet events,
using the correlation between isolated high-transverse energy (E_T>70 GeV)
photons and fully reconstructed jets, based on the information provided by the
CMS calorimeters and silicon tracker.Comment: 4 pages, 4 figures, ontribution to QM'08 conferenc
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