1,262 research outputs found
Tsunamis, Viscosity and the HBT Puzzle
The equation of state and bulk and shear viscosities are shown to be able to
affect the transverse dynamics of a central heavy ion collision. The net
entropy, along with the femtoscopic radii are shown to be affected at the
10-20% level by both shear and bulk viscosity. The degree to which these
effects help build a tsunami-like pulse is also discussed.Comment: Contribution to SQM 2007 in Levoca, Slovaki
Elliptic and triangular flow of identified particles at ALICE
We report on the first measurements of elliptic and triangular flow for
charged pions, kaons and anti-protons in lead-lead collisions at 2.76 TeV
measured with the ALICE detector at the LHC. We compare the observed mass
splitting of differential elliptic flow at LHC energies to RHIC measurements at
lower energies and theory predictions. We test the quark coalescence picture
with the quark number scaling of elliptic and triangular flow.Comment: 4 pages, 5 figures, Quark Matter 2011 conference proceeding
Dissipative hydrodynamics and heavy ion collisions
Space-time evolution and subsequent particle production from minimally
viscous (=0.08) QGP fluid is studied using the 2nd order
Israel-Stewart's theory of dissipative relativistic fluid. Compared to ideal
fluid, energy density or temperature evolves slowly in viscous dynamics.
Particle yield at high is increased. Elliptic flow on the other hand
decreases in viscous dynamics. Minimally viscous QGP fluid found to be
consistent with a large number of experimental data.Comment: 8 pages, 13 figures. Revised version of the invited talk at the 20th
International conference on Ultra-Relativistic Nucleus Nucleus collisions
(Quark Matter 2008), Feb. 4-10, 2008, Jaipur, Indi
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
Centrality dependence of elliptic flow and QGP viscosity
In the Israel-Stewart's theory of second order hydrodynamics, we have
analysed the recent PHENIX data on charged particles elliptic flow in Au+Au
collisions.
PHENIX data demand more viscous fluid in peripheral collisions than in
central collisions. Over a broad range of collision centrality (0-10%- 50-60%),
viscosity to entropy ratio () varies between 0-0.17.Comment: Final version to be publiashed in J. Phys. G. 8 pages, 6 figures and
3 table
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
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
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
Pion electromagnetic form factor at finite temperature
Temperature effects on the electromagnetic couplings of pions in hot hadronic
matter are studied with an effective chiral Lagrangian. We show that the
Ward-Takahashi identity is satisfied at non-zero temperature in the soft pion
limit. The in-medium electromagnetic form factor of the pion is obtained in the
time-like region and shown to be reduced in magnitude, especially near the
vector-meson resonance region. Finally, we discuss the consequences of this
medium effect on dilepton production from hot hadronic matter.Comment: 29 pages (LaTex) + 11 figure
Anisotropic flow at the LHC measured with the ALICE detector
The ALICE detector at the LHC recorded first Pb-Pb collisions at 2.76 TeV in
November and December of 2010. We report on the measurements of anisotropic
flow for charged and identified particles. From the comparison with
measurements at lower energies and with model predictions we find that the
system created at these collision energies is described well by hydrodynamical
model calculations and behaves like an almost perfect fluid.Comment: 8 pages, 16 figures, plenary talk at Quark Matter 2011, May 23rd-28th
2011, Annecy, Franc
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