10,523 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

### Momentum anisotropies in the quark coalescence model

Based on the quark coalescence model, we derive relations among the momentum
anisotropies of mesons and baryons in relativistic heavy ion collisions from a
given, but arbitrary azimuthal distribution for the partons. Besides the
familiar even Fourier coefficients such as the elliptic flow, we also pay
attention to odd Fourier coefficients such as the directed flow, which has been
observed at finite rapidity even at RHIC energies.Comment: 5 page

### Transverse momentum spectra and elliptic flow in ideal hydrodynamics and geometric scaling

In an ideal hydrodynamic model, with an equation of state where the
confinement-deconfinement transition is a cross-over at $T_{co}=196 MeV$, we
have simulated $\sqrt{s}$=200 GeV Au+Au collisions. Simultaneous description of
the experimental charged particle's $p_T$ spectra and elliptic flow require
that in central (0-10%) Au+Au collisions, initial energy density scales with
the binary collision number density. In less central collisions, experimental
data demand scaling with the participant density. Simulation studies also
indicate that in central collisions viscous effects are minimal.Comment: 4 pages, 3 figures

### Direct photon production from viscous QGP

We simulate direct photon production in evolution of viscous QGP medium.
Photons from Compton and annihilation processes are considered. Viscous effect
on photon production is very strong and reliable simulation is possible only in
a limited $p_T$ range. For minimally viscous fluid $\eta/s$=0.08), direct
photons can be reliably computed only up to $p_T \leq$ 1.3 GeV. With reduced
viscosity ($\eta/s$=0.04), the limit increases to $p_T \leq$2GeV.Comment: 6 pages, 5 figure

### Di-jet hadron pair correlation in a hydrodynamical model with a quenching jet

In jet quenching, a hard QCD parton, before fragmenting into a jet of
hadrons, deposits a fraction of its energy in the medium, leading to suppressed
production of high-$p_T$ hadrons. Assuming that the deposited energy quickly
thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP
fluid. Hydrodynamic evolution and subsequent particle emission depend on the
jet trajectories. Azimuthal distribution of excess $\pi^-$ due to quenching
jet, averaged over all the trajectories, reasonably well reproduce the
di-hadron correlation as measured by the STAR and PHENIX collaboration in
central and in peripheral Au+Au collisions.Comment: 5 pages, 4 figures. Some minor corrections are made in the revised
manuscrip

### 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 $\approx$ 1 fm/c after impact.Comment: 4 pages, 5 figures, proceedings for Quark Matter 9

### 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.

### Consequences of energy conservation in relativistic heavy-ion collisions

Complete characterization of particle production and emission in relativistic
heavy-ion collisions is in general not feasible experimentally. This work
demonstrates, however, that the availability of essentially complete
pseudorapidity distributions for charged particles allows for a reliable
estimate of the average transverse momenta and energy of emitted particles by
requiring energy conservation in the process. The results of such an analysis
for Au+Au collisions at sqrt{s_{NN}}= 130 and 200 GeV are compared with
measurements of mean-p_T and mean-E_T in regions where such measurements are
available. The mean-p_T dependence on pseudorapidity for Au+Au collisions at
130 and 200 GeV is given for different collision centralities.Comment: 8 pages, 8 figures, Submitted to Phys. Rev.

### Classical Strongly Coupled QGP: VII. Shear Viscosity and Self Diffusion

We construct the Liouville operator for the SU(2) classical colored Coulomb
plasma (cQGP) for arbitrary values of the Coulomb coupling $\Gamma=V/K$, the
ratio of the mean Coulomb to kinetic energy. We show that its resolvent in the
classical colored phase space obeys a hierarchy of equations. We use a free
streaming approximation to close the hierarchy and derive an integral equation
for the time-dependent structure factor. Its reduction by projection yields
hydrodynamical equations in the long-wavelength limit. We discuss the character
of the hydrodynamical modes at strong coupling. The shear viscosity is shown to
exhibit a minimum at $\Gamma\approx 8$ near the liquid point. This minimum
follows from the cross-over between the single particle collisional regime
which drops as $1/\Gamma^{5/2}$ and the hydrodynamical collisional regime which
rises as $\Gamma^{1/2}$. The self-diffusion constant drops as $1/\Gamma^{3/2}$
irrespective of the regime. We compare our results to molecular dynamics
simulations of the SU(2) colored Coulomb plasma. We also discuss the relevance
of our results for the quantum and strongly coupled quark gluon plasma (sQGP)Comment: 36 pages, 14 figure

### Conservation Laws and the Multiplicity Evolution of Spectra at the Relativistic Heavy Ion Collider

Transverse momentum distributions in ultra-relativistic heavy ion collisions
carry considerable information about the dynamics of the hot system produced.
Direct comparison with the same spectra from $p+p$ collisions has proven
invaluable to identify novel features associated with the larger system, in
particular, the "jet quenching" at high momentum and apparently much stronger
collective flow dominating the spectral shape at low momentum. We point out
possible hazards of ignoring conservation laws in the comparison of high- and
low-multiplicity final states. We argue that the effects of energy and momentum
conservation actually dominate many of the observed systematics, and that $p+p$
collisions may be much more similar to heavy ion collisions than generally
thought.Comment: 15 pages, 14 figures, submitted to PRC; Figures 2,4,5,6,12 updated,
Tables 1 and 3 added, typo in Tab.V fixed, appendix B partially rephrased,
minor typo in Eq.B1 fixed, minor wording; references adde

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