1,792 research outputs found
Constraints on models for the initial collision geometry in ultra relativistic heavy ion collisions
Monte Carlo (MC) simulations are used to compute the centrality dependence of
the collision zone eccentricities (), for both spherical and
deformed ground state nuclei, for different model scenarios. Sizable model
dependent differences are observed. They indicate that measurements of the
and order Fourier flow coefficients ,
expressed as the ratio , can provide robust constraints
for distinguishing between different theoretical models for the initial-state
eccentricity. Such constraints could remove one of the largest impediments to a
more precise determination of the specific viscosity from precision
measurements at the Relativistic Heavy Ion Collider (RHIC).Comment: 4 pages, 3 figs - version accepted for publicatio
Measurement of elliptic and higher order flow harmonics at TeV Pb+Pb collisions with the ATLAS Detector
The measurements of flow harmonics - using the event plane and two
particle correlations methods in broad , and centrality ranges
using the ATLAS detector at LHC are presented. ATLAS recorded about 9 of lead-lead collision data in the 2010 heavy ion run. The
full azimuthal acceptance of the ATLAS detector in units of
pseudorapidity for charged hadrons and the large amount of data allows for a
detailed study of the flow harmonics. The , centrality and ranges
where the two methods give consistent and where they disagree are
discussed. It is shown that the ridge as well as the so called "mach-cone" seen
in two particle correlations are largely accounted for by the collective flow.
Some scaling relations in the dependence of the are also discussed
Azimuthal anisotropy: transition from hydrodynamic flow to jet suppression
Measured 2nd and 4th azimuthal anisotropy coefficients v_{2,4}(N_{part}),
p_T) are scaled with the initial eccentricity \varepsilon_{2,4}(N_{part}) of
the collision zone and studied as a function of the number of participants
N_{part} and the transverse momenta p_T. Scaling violations are observed for
p_T \alt 3 GeV/c, consistent with a dependence of viscous corrections
and a linear increase of the relaxation time with . These empirical
viscous corrections to flow and the thermal distribution function at freeze-out
constrain estimates of the specific viscosity and the freeze-out temperature
for two different models for the initial collision geometry. The apparent
viscous corrections exhibit a sharp maximum for p_T \agt 3 GeV/c, suggesting
a breakdown of the hydrodynamic ansatz and the onset of a change from
flow-driven to suppression-driven anisotropy.Comment: 5 pages, 4 figs; submitted for publicatio
Energy loss for heavy quarks in relation to light partons; is radiative energy loss for heavy quarks anomalous?
The scaling properties of jet suppression measurements are compared for
non-photonic electrons () and neutral pions () in Au + Au
collisions at GeV. For a broad range of transverse momenta
and collision centralities, the comparison is consistent with jet quenching
dominated by radiative energy loss for both heavy and light partons. Less
quenching is indicated for heavy quarks via ; this gives an
independent estimate of the transport coefficient that agrees with
its magnitude obtained from quenching of light partons via 's.Comment: Published versio
Understanding jet quenching and medium response with di-hadron correlation
A brief review of the dependence of the dihadron correlations from RHIC
is presented. We attempt to construct a consistent picture that can describe
the data as a whole, focusing on the following important aspects, 1) the
relation between jet fragmentation of survived jet and medium response to
quenched jets, 2) the possible origin of the medium response and its relation
to intermediate physics for single hadron production, 3) the connection
between the near-side ridge and away-side cone, 4) and their relations to low
energy results.Comment: 8 pages, 8 figures, presented at the 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 2008. Updated with the published versio
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
Elliptic flow of electrons from heavy-flavor hadron decays in Au+Au collisions at 200, 62.4, and 39 GeV
We present measurements of elliptic flow () of electrons from the decays
of heavy-flavor hadrons () by the STAR experiment. For Au+Au collisions
at 200 GeV we report , for transverse momentum
() between 0.2 and 7 GeV/c using three methods: the event plane method
({EP}), two-particle correlations ({2}), and four-particle
correlations ({4}). For Au+Au collisions at = 62.4 and
39 GeV we report {2} for GeV/c. {2} and {4} are
non-zero at low and intermediate at 200 GeV, and {2} is consistent
with zero at low at other energies. The {2} at the two lower beam
energies is systematically lower than at 200 GeV for
GeV/c. This difference may suggest that charm quarks interact less
strongly with the surrounding nuclear matter at those two lower energies
compared to GeV.Comment: Version accepted by PR
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