217 research outputs found
Microscopic Reaction Dynamics at SPS and RHIC
The current status of transport theoretical models applicable to the physics
of the Relativistic Heavy-Ion Collider is reviewed. The time evolution of
microscopic reaction dynamics - from early, hard, partonic rescattering up to
soft hadronic interactions close to freeze-out is analyzed and key observables
linked to the different reaction stages are discussed.Comment: 7 pages, 5 figures, invited talk given at the 15th International
Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (QM 2001), Long
Island, New York, January 15 - 20, 2001, to be published in Nucl. Phy
Shear-Viscosity to Entropy Density Ratio of a Relativistic Hadron Gas
Ultrarelativistic heavy-ion collisions at the Relativistic Heavy-Ion Collider
(RHIC) are thought to have produced a state of matter called the
Quark-Gluon-Plasma, characterized by a very small shear viscosity to entropy
density ratio , near the lower bound predicted for that quantity by
Anti-deSitter space/Conformal Field Theory (AdS/CFT) methods. As the produced
matter expands and cools, it evolves through a phase described by a hadron gas
with rapidly increasing . We calculate as a function of
temperature in this phase and find that its value poses a challenge for viscous
relativistic hydrodynamics, which requires small values of throughout
the entire evolution of the reaction in order to successfully describe the
collective flow observables at RHIC. We show that the inclusion of non-unit
fugacities will reduce in the hadronic phase, yet not sufficiently to
be compatible with viscous hydrodynamics. We therefore conclude that the origin
of the low viscosity matter at RHIC must be in the partonic phase of the
reaction.Comment: 4 pages, 4 figures: Modified figures and revised discussion of
entropy calculatio
Longitudinal Broadening of Quenched Jets in Turbulent Color Fields
The near-side distribution of particles at intermediate transverse momentum,
associated with a high momentum trigger hadron produced in a high energy
heavy-ion collision, is broadened in rapidity compared with the jet cone. This
broadened distribution is thought to contain the energy lost by the progenitor
parton of the trigger hadron. We show that the broadening can be explained as
the final-state deflection of the gluons radiated from the hard parton inside
the medium by soft, transversely oriented, turbulent color fields that arise in
the presence of plasma instabilities. The magnitude of the effect is found to
grow with medium size and density and diminish with increasing energy of the
associated hadron.Comment: 4 pages, 2 figures, Revtex4, revised version, improved abstract and
introductio
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