14 research outputs found
Hadronic dissipative effects on transverse dynamics at RHIC
We simulate the dynamics of Au+Au collisions at the Relativistic Heavy Ion
Collider (RHIC) with a hybrid model that treats the quark-gluon plasma
macroscopically as an ideal fluid, but models the hadron resonance gas
microscopically using a hadronic cascade. We find that much of the
mass-ordering pattern for v_2(p_T) observed at RHIC is generated during the
hadronic stage due to build-up of additional radial flow. We also find that the
mass-ordering pattern is violated for phi meson due to small interaction cross
section in the hadron resonance gas.Comment: 4 pages, 4 figures. To be published in the proceedings of Quark
Matter 2008, Jaipur, Indi
Energy loss in high energy heavy ion collisions from the Hydro+Jet model
We investigate the effect of energy loss of jets in high energy heavy ion
collisions by using a full three-dimensional space-time evolution of a fluid
combined with (mini-)jets that are explicitly evolved in space-time. In order
to fit the pi^0 data for the Au+Au collisions at sqrt(s_{NN}) = 130 GeV, the
space-time averaged energy loss dE/dx(tau <= 3 fm/c) = 0.36 GeV/fm is extracted
within the model. It is found that most energy loss occurs at the very early
time less than 2 fm/c in the QGP phase and that energy loss in the mixed phase
is negligible within our parameterization for jet energy loss. This is a
consequence of strong expansion of the system.Comment: 4 pages, 5 figures; one figure adde
Temperature dependent sound velocity in hydrodynamic equations for relativistic heavy-ion collisions
We analyze the effects of different forms of the sound-velocity function
cs(T) on the hydrodynamic evolution of matter formed in the central region of
relativistic heavy-ion collisions. At high temperatures (above the critical
temperature Tc) the sound velocity is calculated from the recent lattice
simulations of QCD, while in the low temperature region it is obtained from the
hadron gas model. In the intermediate region we use different interpolations
characterized by the values of the sound velocity at the local maximum (at T =
0.4 Tc) and local minimum (at T = Tc). In all considered cases the temperature
dependent sound velocity functions yield the entropy density, which is
consistent with the lattice QCD simulations at high temperature. Our
calculations show that the presence of a distinct minimum of the sound velocity
leads to a very long (about 20 fm/c) evolution time of the system, which is not
compatible with the recent estimates based on the HBT interferometry. Hence, we
conclude that the hydrodynamic description is favored in the case where the
cross-over phase transition renders the smooth sound velocity function with a
possible shallow minimum at Tc.Comment: 6 pages, 3 figures, talk given at SQM'07 Levoca, Slovaki
Feeding of the elliptic flow by hard partons
We propose that in nuclear collisions at the LHC the elliptic flow may get a
contribution from leading hard and semihard partons which deposit energy and
momentum into the hydrodynamic bulk medium. The crucial effect is that these
partons induce wakes which interact and merge if they come together. The
contribution to the integrated elliptic flow is estimated with the help of a
toy model to about 25% of the observed value and shows strong event-by-event
fluctuations.Comment: 9 pages, 3 figure
Elliptic Flow: A Brief Review
One of the fundamental questions in the field of subatomic physics is what
happens to matter at extreme densities and temperatures as may have existed in
the first microseconds after the Big Bang and exists, perhaps, in the core of
dense neutron stars. The aim of heavy-ion physics is to collide nuclei at very
high energies and thereby create such a state of matter in the laboratory. The
experimental program started in the 1990's with collisions made available at
the Brookhaven Alternating Gradient Synchrotron (AGS), the CERN Super Proton
Synchrotron (SPS) and continued at the Brookhaven Relativistic Heavy-Ion
Collider (RHIC) with maximum center of mass energies of 4.75, 17.2 and 200 GeV
respectively. Collisions of heavy-ions at the unprecedented energy of 2.76 TeV
have recently become available at the LHC collider at CERN. In this review I
will give a brief introduction to the physics of ultra-relativistic heavy-ion
collisions and discuss the current status of elliptic flow measurements.Comment: version accepted by NJ
Hydrodynamic afterburner for the CGC at RHIC
Firstly, we give a short review about the hydrodynamic model and its
application to the elliptic flow phenomena in relativistic heavy ion
collisions. Secondly, we show the first approach to construct a unified model
for the description of the dynamics in relativistic heavy ion collisions.Comment: 15 pages, 7 figures, invited talk presented at "Hot Quarks 2004",
July 18-24, 2004, Taos Valley, NM, US
Quark-Gluon Plasma at RHIC and the LHC: Perfect Fluid too Perfect?
Relativistic heavy ion collisions have reached energies that enable the
creation of a novel state of matter termed the quark-gluon plasma. Many
observables point to a picture of the medium as rapidly equilibrating and
expanding as a nearly inviscid fluid. In this article, we explore the evolution
of experimental flow observables as a function of collision energy and attempt
to reconcile the observed similarities across a broad energy regime in terms of
the initial conditions and viscous hydrodynamics. If the initial spatial
anisotropies are very similar for all collision energies from 39 GeV to 2.76
TeV, we find that viscous hydrodynamics might be consistent with the level of
agreement for v2 of unidentified hadrons as a function of pT . However, we
predict a strong collision energy dependence for the proton v2(pT). The results
presented in this paper highlight the need for more systematic studies and a
re-evaluation of previously stated sensitivities to the early time dynamics and
properties of the medium.Comment: 11 pages, 9 figures, submitted to the New Journal of Physics focus
issue "Strongly Correlated Quantum Fluids: From Ultracold Quantum Gases to
QCD Plasmas
Jet tomography
I summarize the recent advances in jet tomographic studies of cold and hot
nuclear matter based on perturbative QCD calculations of medium-induced gluon
bremsstrahlung. Quantitative applications to ultrarelativistic heavy ion
reactions at RHIC indicate the creation of a deconfined state of QCD with
initial energy density on the order of 100 times cold nuclear matter density.Comment: Plenary talk given at the seventeenth international conference on
Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004). 8 pages,
12 figures. Updated references, updated Table
Particlization in hybrid models
In hybrid models, which combine hydrodynamical and transport approaches to
describe different stages of heavy-ion collisions, conversion of fluid to
individual particles, particlization, is a non-trivial technical problem. We
describe in detail how to find the particlization hypersurface in a 3+1
dimensional model, and how to sample the particle distributions evaluated using
the Cooper-Frye procedure to create an ensemble of particles as an initial
state for the transport stage. We also discuss the role and magnitude of the
negative contributions in the Cooper-Frye procedure.Comment: 18 pages, 28 figures, EPJA: Topical issue on "Relativistic Hydro- and
Thermodynamics"; version accepted for publication, typos and error in Eq.(1)
corrected, the purpose of sampling and change from UrQMD to fluid clarified,
added discussion why attempts to cancel negative contributions of Cooper-Frye
are not applicable her
Flow in heavy-ion collisions - Theory Perspective
I review recent developments in the field of relativistic hydrodynamics and
its application to the bulk dynamics in heavy-ion collisions at the
Relativistic Heavy- Ion Collider (RHIC) and the Large Hadron Collider (LHC). In
particular, I report on progress in going beyond second order relativistic
viscous hydrodynamics for conformal fluids, including temperature dependent
shear viscosity to entropy density ratios, as well as coupling hydrodynamic
calculations to microscopic hadronic rescattering models. I describe
event-by-event hydrodynamic simulations and their ability to compute higher
harmonic flow coefficients. Combined comparisons of all harmonics to recent
experimental data from both RHIC and LHC will potentially allow to determine
the desired details of the initial state and the medium properties of the
quark-gluon plasma produced in heavy-ion collisions.Comment: 8 pages, Invited plenary talk at the 22nd International Conference on
Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2011), May 23-28
2011, Annecy, Franc