Folie 1

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Johann Wolfgang Goethe-Universität Frankfurt
Institut für Theoretische Physik
The role of the gluonic gglt-gtggg interactions in
early thermalization
Zhe Xu

• Motivation
• Theory and Results
• Summary and outlook

HQ2006
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Motivation
elliptic flow --- early signature of QGP
evidence for an early buildup of pressure and a
fast thermalization of the quark-gluon system
transport simulation on-shell parton cascade
Z. Xu and C. Greiner, PRC 71, 064901 (2005)
solving the Boltzmann-equations for quarks and
gluons
new development
(Z)MPC, VNI/BMS
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parton scatterings in leading order pQCD
J.F.Gunion, G.F.Bertsch, Phys. Rev. D 25,
746(1982)
screening mass
LPM suppression the formation time
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Simulation 1
thermalization and hydrodynamical behavior
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Simulation 1
Simulation 2
thermalization and hydrodynamical behavior
NO thermalization and free
streaming
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Simulation 1
Simulation 2
thermalization and hydrodynamical behavior
NO thermalization and free
streaming
Question Why are gglt-gtggg interactions
essential for thermalization?
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(at chemical equilibrium)
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old idea transport cross section
where
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old idea transport cross section
wrong !
where
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at chemical equilibrium
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Theory and Results
Definition
Boltzmann equation
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The drift term is large.
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special case
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Assume chemical equilibrium
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Summary
PQCD Bremsstrahlung gg?ggg are essential for the
thermalization.
Old idea about the transport cross section is
wrong.
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collision angle and transport cross section
transport cross section
gg -gt gg
gg -gt ggg
LPM suppression
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P.Danielewicz, G.F.Bertsch, Nucl. Phys. A 533,
712(1991) A.Lang et al., J. Comp. Phys. 106,
391(1993)
Stochastic algorithm
cell configuration in space
D3x
for particles in D3x with momentum p1,p2,p3 ...
collision probability
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Initial conditions minijets production with pt gt
p0
binary approximation ?
for a central AuAu collision at RHIC at 200 AGeV
using p02 GeV
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Initial conditions with smaller p0
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Kinetic and chemical equilibration
in the central region h -0.50.5 and xt lt 1.5
fm
12 fm/c for the kinetic equilibration
4 fm/c for the chemical equilibration
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Kinetic and chemical equilibration
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transverse energy at y0 in AuAu central
collision
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Initial condition with Color Glass Condensate
h -0.050.05 and xt lt 1.5 fm
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Kinetic and chemical equilibration
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elliptic flow in noncentral AuAu collisions at
RHIC
peripheral
central
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Comparison with RHIC data
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Jet-Quenching in a central Au Au collision at RHIC
34 too much
by Oliver Fochler