3,627 research outputs found
High-energy dileptons from an anisotropic quark-gluon plasma
We calculate leading-order dilepton yields from a quark-gluon plasma which
has a time-dependent anisotropy in momentum space. Such anisotropies can arise
during the earliest stages of quark-gluon plasma evolution due to the rapid
longitudinal expansion of the created matter. A phenomenological model for the
proper time dependence of the parton hard momentum scale, p_hard, and the
plasma anisotropy parameter, xi, is proposed. The model describes the
transition of the plasma from a 0+1 dimensional collisionally-broadened
expansion at early times to a 0+1 dimensional ideal hydrodynamic expansion at
late times. We find that high-energy dilepton production is enhanced by
pre-equilibrium emission up to 50% at LHC energies, if one assumes an
isotropization/thermalization time of 2 fm/c. Given sufficiently precise
experimental data this enhancement could be used to determine the plasma
isotropization time experimentally.Comment: 13 pages, 5 figures, talk given at the 4th international workshop on
High-pT Physics at the LHC 09, February 4-7 2009, Prague, Czech Republic.
Accepted to the proceedings of 4th international workshop High-pT physics at
LHC 0
Measuring Quark-Gluon-Plasma Thermalization Time with Dileptons
We calculate the medium dilepton yield from a quark-gluon plasma which has a
time-dependent local momentum-space anisotropy. A phenomenological model for
the hard momentum scale, p_hard(tau), and plasma anisotropy parameter, xi(tau),
is constructed which interpolates between free streaming behavior at early
times (tau >
tau_iso). We show that high-energy dilepton production is sensitive to the
assumed plasma isotropization time, tau_iso, and can therefore be used to
experimentally determine the time of onset for hydrodynamic expansion of a
quark-gluon plasma and the magnitude of expected early-time momentum-space
anisotropies.Comment: 4 pages, 5 figures; v3: update to match published versio
Fluid dynamic propagation of initial baryon number perturbations on a Bjorken flow background
Baryon number density perturbations offer a possible route to experimentally
measure baryon number susceptibilities and heat conductivity of the quark gluon
plasma. We study the fluid dynamical evolution of local and event-by-event
fluctuations of baryon number density, flow velocity and energy density on top
of a (generalized) Bjorken expansion. To that end we use a
background-fluctuation splitting and a Bessel-Fourier decomposition for the
fluctuating part of the fluid dynamical fields with respect to the azimuthal
angle, the radius in the transverse plane and rapidity. We examine how the time
evolution of linear perturbations depends on the equation of state as well as
on shear viscosity, bulk viscosity and heat conductivity for modes with
different azimuthal, radial and rapidity wave numbers. Finally we discuss how
this information is accessible to experiments in terms of the transverse and
rapidity dependence of correlation functions for baryonic particles in high
energy nuclear collisions.Comment: 36 pages, 11 figures; v3: change in the format of the latex file.
Minor changes in the text. Typos corrected and updated references. Tweak in
Fig. 1-11. Accepted for publication in Phys. Rev.
Boost-Invariant (2+1)-dimensional Anisotropic Hydrodynamics
We present results of the application of the anisotropic hydrodynamics
(aHydro) framework to (2+1)-dimensional boost invariant systems. The necessary
aHydro dynamical equations are derived by taking moments of the Boltzmann
equation using a momentum-space anisotropic one-particle distribution function.
We present a derivation of the necessary equations and then proceed to
numerical solutions of the resulting partial differential equations using both
realistic smooth Glauber initial conditions and fluctuating Monte-Carlo Glauber
initial conditions. For this purpose we have developed two numerical
implementations: one which is based on straightforward integration of the
resulting partial differential equations supplemented by a two-dimensional
weighted Lax-Friedrichs smoothing in the case of fluctuating initial
conditions; and another that is based on the application of the Kurganov-Tadmor
central scheme. For our final results we compute the collective flow of the
matter via the lab-frame energy-momentum tensor eccentricity as a function of
the assumed shear viscosity to entropy ratio, proper time, and impact
parameter.Comment: 45 pages, 12 figures; v2 published versio
Constraining the onset of viscous hydrodynamics
We derive two general criteria that can be used to constrain the initial time
of the onset of 2nd-order conformal viscous hydrodynamics in relativistic
heavy-ion collisions. We show this explicitly for 0+1 dimensional viscous
hydrodynamics and discuss how to extend the constraint to higher dimensions.Comment: 2 pages, 2 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee. Selected Poster
for the Flash Talk Session at QM09. v3: typos corrected, minor format changes
and updated reference
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