906 research outputs found
Is there elliptic flow without transverse flow?
Azimuthal anisotropy of final particle distributions was originally
introduced as a signature of transverse collective flow. We show that finite
anisotropy in momentum space can result solely from the shape of the particle
emitting source. However, by comparing the differential anisotropy to recent
data from STAR collaboration we can exclude such a scenario, but instead show
that the data favour strong flow as resulting from a hydrodynamical evolution.Comment: To appear in proceedings of Quark Matter 2001, 4 pages LaTeX, uses
espcrc1.st
Evolution of pion HBT radii from RHIC to LHC -- Predictions from ideal hydrodynamics
We present hydrodynamic predictions for the charged pion HBT radii for a
range of initial conditions covering those presumably reached in Pb+Pb
collisions at the LHC. We study central (b=0) and semi-central (b=7fm)
collisions and show the expected increase of the HBT radii and their azimuthal
oscillations. The predicted trends in the oscillation amplitudes reflect a
change of the final source shape from out-of-plane to in-plane deformation as
the initial entropy density is increased.Comment: 6 pages, incl. 5 figures. Contribution to the CERN Theory Institute
Workshop "Heavy Ion Collisions at the LHC -- Last Call for Predictions",
CERN, 14 May - 8 June 2007, to appear in J. Phys.
Equation of State and Collective Dynamics
This talk summarizes the present status of a program to quantitatively relate
data from the Relativistic Heavy Ion Collider (RHIC) on collective expansion
flow to the Equation of State (EOS) of hot and dense strongly interacting
matter, including the quark-gluon plasma and the quark-hadron phase transition.
The limits reached with the present state of the art and the next steps
required to make further progress will both be discussed.Comment: 8 pages, 6 two-part figures. Invited talk given at the 5th
International Conference on the Physics and Astrophysics of Quark-Gluon
Plasma (ICPAQGP 2005), Kolkata (India), Feb 8-12, 2005. Proceedings to be
published in Journal of Physics: Conference Series (Jan-E Alam et al., eds.
Hydrodynamic simulation of elliptic flow
We use a hydrodynamic model to study the space-time evolution transverse to
the beam direction in ultrarelativistic heavy-ion collisions with nonzero
impact parameters. We focus on the influence of early pressure on the
development of radial and elliptic flow. We show that at high energies elliptic
flow is generated only during the initial stages of the expansion while radial
flow continues to grow until freeze-out. Quantitative comparisons with SPS data
from semiperipheral Pb+Pb collisions suggest the applicability of
hydrodynamical concepts already 1 fm/c after impact.Comment: 4 pages, 5 figures, proceedings for Quark Matter 9
Fitted HBT radii versus space-time variances in flow-dominated models
The inability of otherwise successful dynamical models to reproduce the ``HBT
radii'' extracted from two-particle correlations measured at the Relativistic
Heavy Ion Collider (RHIC) is known as the ``RHIC HBT Puzzle.'' Most comparisons
between models and experiment exploit the fact that for Gaussian sources the
HBT radii agree with certain combinations of the space-time widths of the
source which can be directly computed from the emission function, without
having to evaluate, at significant expense, the two-particle correlation
function. We here study the validity of this approach for realistic emission
function models some of which exhibit significant deviations from simple
Gaussian behaviour. By Fourier transforming the emission function we compute
the 2-particle correlation function and fit it with a Gaussian to partially
mimic the procedure used for measured correlation functions. We describe a
novel algorithm to perform this Gaussian fit analytically. We find that for
realistic hydrodynamic models the HBT radii extracted from this procedure agree
better with the data than the values previously extracted from the space-time
widths of the emission function. Although serious discrepancies between the
calculated and measured HBT radii remain, we show that a more
``apples-to-apples'' comparison of models with data can play an important role
in any eventually successful theoretical description of RHIC HBT data.Comment: 12 pages, 16 color figure
Photon HBT interferometry for non-central heavy-ion collisions
Currently, the only known way to obtain experimental information about the
space-time structure of a heavy-ion collision is through 2-particle momentum
correlations. Azimuthally sensitive HBT interferometry (Hanbury Brown-Twiss
intensity interferometry) can complement elliptic flow measurements by
constraining the spatial deformation of the source and its time evolution.
Performing these measurements on photons allows us to access the fireball
evolution at earlier times than with hadrons. Using ideal hydrodynamics to
model the space-time evolution of the collision fireball, we explore
theoretically various aspects of 2-photon intensity interferometry with
transverse momenta up to 2 GeV, in particular the azimuthal angle dependence of
the HBT radii in non-central collisions. We highlight the dual nature of
thermal photon emission, in both central and non-central collisions, resulting
from the superposition of QGP and hadron resonance gas photon production. This
signature is present in both the thermal photon source function and the HBT
radii extracted from Gaussian fits of the 2-photon correlation function.Comment: 18 pages, 12 figure
Hydrodynamic emission of strange and non-strange particles at RHIC and LHC
The hydrodynamic model is used to describe the single-particle spectra and
elliptic flow of hadrons at RHIC and to predict the emission angle dependence
of HBT correlations at RHIC and LHC energies.Comment: 6 pages LaTeX, 3 postscript figures. Proceedings for the conference
"Strange Quark Matter 2003", Atlantic Beach, NC, March 12-17, 2003, to appear
in J. Phys.
Charmonia enhancement in quark-gluon plasma with improved description of c-quarks phase-distribution
We present a dynamical model of heavy quark evolution in the quark-gluon
plasma (QGP) based on the Fokker-Planck equation. We then apply this model to
the case of central ultra-relativistic nucleus-nucleus collisions performed at
RHIC and estimate the component of production (integrated and
differential) stemming from c- pairs that are initially uncorrelated.Comment: contribution presented at SQM0
Dynamical freeze-out condition in ultrarelativistic heavy ion collisions
We determine the decoupling surfaces for the hydrodynamic description of
heavy ion collisions at RHIC and LHC by comparing the local hydrodynamic
expansion rate with the microscopic pion-pion scattering rate. The pion
spectra for nuclear collisions at RHIC and LHC are computed by applying the
Cooper-Frye procedure on the dynamical-decoupling surfaces, and compared with
those obtained from the constant-temperature freeze-out surfaces. Comparison
with RHIC data shows that the system indeed decouples when the expansion rate
becomes comparable with the pion scattering rate. The dynamical decoupling
based on the rates comparison also suggests that the effective decoupling
temperature in central heavy ion collisions remains practically unchanged from
RHIC to LHC.Comment: 7 pages, 9 figure
Radial flow afterburner for event generators and the baryon puzzle
A simple afterburner including radial flow to the randomized transverse
momentum obtained from event generators, Pythia and Hijing, has been
implemented to calculate the ratios and compare them with available
data. A coherent trend of qualitative agreement has been obtained in
collisions and in for various centralities. Those results indicate that
the radial flow does play an important role in the so called baryon puzzle
anomaly.Comment: 11 pages, 5 figures. To appear in Journal of Physics
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