Speaker
Huichao Song
(The Ohio State Univ)
Description
The viscosity of the QGP is a presently hotly debated subject.
Since its computation from first principles is difficult, it is desirable
to try to extract it from experimental data. Viscous hydrodynamics
provides a tool that can attack this problem and which may work in regions
where ideal hydrodynamics begins to fail.\\
Through the efforts of different groups, the elliptic flow has now
been widely accepted as the key observable to constrain the QGP
shear viscosity. During the last year, several groups have developed
numerical codes to solve the equations of causal relativistic fluid
dynamics and published first results. We will report on the work of
the Ohio State University group on setting up the equations for
causal viscous hydrodynamics in 2+1 dimensions [1] and solving them
numerically for central and noncentral Cu+Cu and Au+Au collisions at
RHIC energies and above. We will discuss shear and bulk viscous
effects on the hydrodynamic evolution of energy density,
temperature, collective flow, and flow anisotropies, and on the
hadron multiplicity, single particle spectra and elliptic flow
[2-5]. The dynamical effects of using different versions of the
Israel-Stewart second order formalism for causal viscous fluid
dynamics will be discussed, resolving the origins of some apparent
discrepancies between early results reported by different groups
[4]. Viscous entropy production and its influence on the centrality
dependence of hadron multiplicities and the multiplicity scaling of
eccentricity-scaled elliptic flow will be studied in viscous
hydrodynamics [4] and compared with experimental data. The present
status of constraining the shear viscosity to entropy ratio of the
hot and dense matter created at RHIC will be assessed[5].
[1] U.~Heinz, H.~Song and A.~K.~Chaudhuri,\emph{``Dissipative
hydrodynamics for viscous relativistic fluids,''} Phys. Rev. {\bf C
73}, 034904 (2006)
[2] H.~Song and U.~Heinz, \emph{``Suppression of elliptic flow in a minimally viscous quark-gluon plasma,''} Phys. Lett. B {\bf658}, 279 (2008).
[3] H.~Song and U.~Heinz, \emph{``Causal viscous hydrodynamics in 2+1 dimensions for relativistic heavy-ion collisions,''} Phys. Rev. {\bf C 77}, 064901 (2008).
[4] H.~Song and U.~Heinz, \emph{``Multiplicity scaling in ideal and
viscous hydrodynamics,''} Phys. Rev. {\bf C78}, 024902,2008.
[5] H.~Song and U. Heinz, \emph{``Extracting the QGP viscosity from
RHIC data - A Status report from viscous hydrodynamics''} J. Phys.
G, in press [arXiv:0812.4274 [nucl-th]].
Author
Huichao Song
(The Ohio State Univ)
