109 research outputs found
Jet-Tagged Back-Scattering Photons For Quark Gluon Plasma Tomography
Several sources of direct photons are known to contribute to the total photon
yield in high energy nuclear collisions. All of these photons carry
characteristic and important information on the initial nuclei or the hot and
dense fireball created in the collision. We investigate the possibility to
separate photons from back-scattering of high momentum quarks off quark gluon
plasma from other sources. Their unique kinematics can be utilized through high
energy jet triggers on the away-side. We discuss the basic idea and estimate
the feasibility of such a measurement at RHIC and LHC.Comment: Contribution to Hard Probes 2012; 4 pages, 4 figure
Azimuthal Asymmetry of Direct Photons in High Energy Nuclear Collisions
We show that a sizeable azimuthal asymmetry, characterized by a coefficient
v_2, is to be expected for direct photons produced in non-central high energy
nuclear collisions. This signal is generated by photons radiated by jets
interacting with the surrounding hot plasma. The anisotropy is out of phase by
an angle with respect to that associated with the elliptic anisotropy
of hadrons, leading to negative values of v_2. Such an asymmetry, if observed,
could be a signature for the presence of a quark gluon plasma and would
establish the importance of jet-plasma interactions as a source of
electromagnetic radiation.Comment: New title. Final versio
Measurement of photons via conversion pairs in \sqrt{s_{NN}} = 200 GeV Au+Au collisions with the PHENIX experiment at RHIC
Thermal photons can provide information on the temperature of the new state
of matter created at RHIC. In the p_T region of 1--3 GeV/c thermal photons are
expected to be the dominant direct photon source. Therefore, a possible excess
compared to a pure decay photon signal due to a thermal photon contribution
should be seen in the double ratio
(\gamma/\gamma(\pi^{0}))_{Measured}/(\gamma/\gamma(\pi^{0}))_{Simulated}, if
sufficient accuracy can be reached. We present a method to reconstruct direct
photons by measuring e^{+}e^{-}--pairs from external photon conversions.Comment: 4 pages, 7 figures. To appear in the proceedings of Hot Quarks 2006:
Workshop for Young Scientists on the Physics of Ultrarelativistic
Nucleus-Nucleus Collisions, Villasimius, Italy, 15-20 May 200
High-pT pi0 Production with Respect to the Reaction Plane Using the PHENIX Detector at RHIC
The origin of the azimuthal anisotropy in particle yields at high pT (pT > 5
GeV/c) in RHIC collisions remains an intriguing puzzle. Traditional flow and
parton energy loss models have failed to completely explain the large v2
observed at high pT. Measurement of this parameter at high pT will help to gain
an understanding of the interplay between flow, recombination and energy loss,
and the role they play in the transition from soft to hard physics. Neutral
mesons measured in the PHENIX experiment provide an ideal observable for such
studies. We present recent measurements of \piz yields with respect to the
reaction plane, and discuss the impact current models have on our understanding
of these mechanisms.Comment: Contribnution to the proceedings of Hot Quarks 2006, 15-20 May 2006,
Villasimius, Sardini
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
Direct photons measured by the PHENIX experiment at RHIC
Results from the PHENIX experiment at RHIC on direct photon production in
p+p, d+Au, and Au+Au collisions at sqrt(s_NN) = 200 GeV are presented. In p+p
collisions, direct photon production at high p_T behaves as expected from
perturbative QCD calculations. The p+p measurement serves as a baseline for
direct photon production in Au+Au collisions. In d+Au collisions, no effects of
cold nuclear matter are found within the large uncertainty of the measurement.
In Au+Au collisions, the production of high p_T direct photons scales as
expected for particle production in hard scatterings. This supports jet
quenching models, which attribute the suppression of high p_T hadrons to the
energy loss of fast partons in the medium produced in the collision. Low p_T
direct photons, measured via e+e- pairs with small invariant mass, are possibly
related to the production of thermal direct photons.Comment: 5 pages, 5 figures, Proceedings of the Hot Quarks 2006 Workshop for
young scientists on the physics of ultra-relativistic nucleus-nucleus
collisions, Villasimius, Sardinia, Italy, May 15--20, 200
Photon production in relativistic nuclear collisions at SPS and RHIC energies
Chiral Lagrangians are used to compute the production rate of photons from
the hadronic phase of relativistic nuclear collisions. Special attention is
paid to the role of the pseudovector a_1 meson. Calculations that include
reactions with strange mesons, hadronic form factors and vector spectral
densities consistent with dilepton production, as well as the emission from a
quark-gluon plasma and primordial nucleon-nucleon collisions, reproduce the
photon spectra measured at the Super Proton Synchrotron (SPS). Predictions for
the Relativistic Heavy Ion Collider (RHIC) are made.Comment: Work presented at the 26th annual Montreal-Rochester-Syracuse-Toronto
conference (MRST 2004) on high energy physics, Montreal, QC, Canada, 12-14
May 2004. 8 pages, 3 figure
Rate of photon production from hot hadronic matter
Thermal photon emission rates from hot hadronic matter are studied to order
, where indicates a strong-interaction coupling constant.
Radiative decay of mesons, Compton and annihilation processes for hadrons, and
bremsstrahlung reactions are all considered. Compared to the standard rates
from the literature, one finds two orders of magnitude increase for low photon
energies stemming mainly from bremsstrahlung and then a modest increase (factor
of 2) for intermediate and high energy photons owing to radiative decays for a
variety of mesons and from other reactions involving strangeness. These results
could have important consequences for electromagnetic radiation studies at
RHIC.Comment: 5 pages LaTeX, 4 Postscript figure
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