75 research outputs found
Electromagnetic Probes in PHENIX
Electromagnetic probes are arguably the most universal tools to study the
different physics processes in high energy hadron and heavy ion collisions. In
this paper we summarize recent measurements of real and virtual direct photons
at central rapidity by the PHENIX experiment at RHIC in p+p, d+Au and Au+Au
collisions. We also discuss the impact of the results and the constraints they
put on theoretical models. At the end we report on the immediate as well as on
the mid-term future of photon measurements at RHIC.Comment: 8 pages, 9 postscript figures, to be published in the Proceedings of
the Hard Probes 2006 conference (June 9-16, 2006, Asilomar, CA
Radiative and Collisional Energy Loss, and Photon-Tagged Jets at RHIC
The suppression of single jets at high transverse momenta in a quark-gluon
plasma is studied at RHIC energies, and the additional information provided by
a photon tag is included. The energy loss of hard jets traversing through the
medium is evaluated in the AMY formalism, by consistently taking into account
the contributions from radiative events and from elastic collisions at leading
order in the coupling. The strongly-interacting medium in these collisions is
modelled with (3+1)-dimensional ideal relativistic hydrodynamics. Putting these
ingredients together with a complete set of photon-production processes, we
present a calculation of the nuclear modification of single jets and
photon-tagged jets at RHIC.Comment: 4 pages, 4 figures, contributed to the 3rd International Conference
on Hard and Electro-Magnetic Probes of High-Energy Nuclear Collisions (Hard
Probes 2008), typos corrected, published versio
Energy Loss of Leading Hadrons and Direct Photon production in Evolving Quark-Gluon Plasma
We calculate the nuclear modification factor of neutral pions and the photon
yield at high p_T in central Au-Au collisions at RHIC (\sqrt{s}=200 GeV) and
Pb-Pb collisions at the LHC (\sqrt{s}=5500 GeV). A leading-order accurate
treatment of jet energy loss in the medium has been convolved with a physical
description of the initial spatial distribution of jets and a (1+1) dimensional
expansion. We reproduce the nuclear modification factor of pion R_{AA} at RHIC,
assuming an initial temperature T_i=370 MeV and a formation time \tau_i=0.26
fm/c, corresponding to dN/dy=1260. The resulting suppression depends on the
particle rapidity density dN/dy but weakly on the initial temperature. The jet
energy loss treatment is also included in the calculation of high p_T photons.
Photons coming from primordial hard N-N scattering are the dominant
contribution at RHIC for p_T > 5 GeV, while at the LHC, the range 8<p_T<14 GeV
is dominated by jet-photon conversion in the plasma.Comment: 21 pages, 16 figures. Discussions and references added. New figure
includind photon dat
Radiative and Collisional Jet Energy Loss in a Quark-Gluon Plasma
We calculate radiative and collisional energy loss of hard partons traversing
the quark-gluon plasma created at RHIC and compare the respective size of these
contributions. We employ the AMY formalism for radiative energy loss and
include additionally energy loss by elastic collisions. Our treatment of both
processes is complete at leading order in the coupling, and accounts for the
probabilistic nature of jet energy loss. We find that a solution of the
Fokker-Planck equation for the probability density distributions of partons is
necessary for a complete calculation of the nuclear modification factor
for pion production in heavy ion collisions. It is found that the
magnitude of is sensitive to the inclusion of both collisional and
radiative energy loss, while the average energy is less affected by the
addition of collisional contributions. We present a calculation of for
at RHIC, combining our energy loss formalism with a relativistic
(3+1)-dimensional hydrodynamic description of the thermalized medium.Comment: 4 pages, 4 figures, contributed to Quark Matter 2008, Jaipur, Indi
Photon Production in Hot and Dense Strongly Interacting Matter
This text is meant as an introduction to the theoretical physics of photon
emission in hot and dense strongly interacting matter, the principal
application being relativistic nuclear collisions. We shall cover some of the
results and techniques appropriate for studies at SPS, RHIC, and LHC energiesComment: 35 pages, accepted for publication, Landolt-Boernstein Volume 1-23
Multiplicity distributions inside parton cascades developing in a medium
The explanation of the suppression of high-pT hadron yields at RHIC in terms
of jet-quenching implies that the multiplicity distributions of particles
inside a jet and jet-like particle correlations differ strongly in
nucleus-nucleus collisions at RHIC or at the LHC from those observed at e+e- or
hadron colliders. We present a framework for describing the medium-induced
modification, which has a direct interpretation in terms of a probabilistic
medium-modified parton cascade, and which treats leading and subleading partons
on an equal footing. We show that our approach can account for the strong
suppression of single inclusive hadron spectra measured in Au-Au collisions at
RHIC, and that this implies a characteristic distortion of the single inclusive
distribution of soft partons inside the jet. We determine, as a function of the
jet energy, to what extent the soft fragments within a jet can be measured
above some momentum cut.Comment: 5 pages, 4 eps-figures; talk given at Hot Quarks 2006, Villasimius
(Sardinia, Italy), May 15-20, 200
Electromagnetic probes
We introduce the seminal developments in the theory and experiments of
electromagnetic probes for the study of the dynamics of relativistic heavy ion
collisions and quark gluon plasma.Comment: 47 pages, 33 Figures; Lectures delivered by Dinesh K. Srivastava at
QGP Winter School (QGPWS08) at Jaipur, India, February 1-3, 200
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