6,270 research outputs found
A Systematic Study on Direct Photon Production from Central Heavy Ion Collisions
We investigate the production of direct photons in central Au-Au collisions
at the relativistic Heavy-Ion Collider (RHIC) at 200 GeV per nucleon,
considering all possible sources. We treat thermal photons emitted from a
quark-gluon plasma and from a hadron gas, based on a realistic thermodynamic
expansion. Hard photons from elementary nucleon-nucleon scatterings are
included: primordial elementary scatterings are certainly dominant at large
transverse momenta, but also secondary photons from jet fragmentation and
jet-photon conversion cannot be ignored. In both cases we study the effect of
energy loss, and we also consider photons emitted from bremsstrahlung gluons
via fragmentation.Comment: 13 pages 19 figure
Another solution to the puzzle of the direct photon elliptic flow
The observed large elliptic flow of direct photons is a puzzle in
relativistic heavy ion physics. Our previous work provided a possibility to
this puzzle with the delayed formation of the quark gluon plasma (QGP) in
relativistic heavy ion collisions. In this work, we got the measured transverse
momentum spectra, elliptic flow v2 and triangular flow v3 of direct photons
from Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) energy
\sqrt s_NN = 200 GeV with all centrality classes explained at the same time
without any additional parameter to EPOS3, a hydrodynamic model which can
successfully reproduce hadronic data such as rapidity distributions, transverse
momenta, elliptic flows and triangular flows from variuos collision systems.
The key point is that, EPOS3 has an initial space eccentricity similar to other
models, however, a stronger radial flow and a weaker momentum eccentrcity made
a good description to the flows of both hadrons and direct photons. The created
QGP matter seems discrete than a soup.Comment: 7 pages 8 fig
Anisotropic emission of thermal dielectrons from Au+Au collisions at ~GeV with EPOS3
Dileptons, as an electromagnetic probe, are crucial to study the properties
of a Quark-Gluon Plasma (QGP) created in heavy ion collisions. We calculated
the invariant mass spectra and the anisotropic emission of thermal dielectrons
from Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) energy
~GeV based on EPOS3. This approach provides a realistic
(3+1)-dimensional event-by-event viscous hydrodynamic description of the
expanding hot and dense matter with a very particular initial condition, and a
large set of hadron data and direct photons (besides and !) can
be successfully reproduced. Thermal dilepton emission from both the QGP phase
and the hadronic gas are considered, with the emission rates based on Lattice
QCD and a vector meson model, respectively. We find that the computed invariant
mass spectra (thermal contribution + STAR cocktail) can reproduce the measured
ones from STAR at different centralities. Different compared to other model
predictions, the obtained elliptic flow of thermal dileptons is larger than the
STAR measurement referring to all dileptons. We observe a clear centrality
dependence of thermal dilepton not only for elliptic flow but also for
higher orders. At a given centrality, of thermal dileptons decreases
monotonically with for .Comment: 10pages, 12fig
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