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Zhe Xu

Johann Wolfgang Goethe-Universität Frankfurt Institut für Theoretische Physik. Parton Thermalization and Energy Loss in ultrarelativistic Heavy-Ion Collisions within a Parton Cascade. Zhe Xu. in collaboration with A. El, O.Fochler and C.Greiner. QM2006, Shang Hai. Motivation.

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Zhe Xu

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  1. Johann Wolfgang Goethe-Universität Frankfurt Institut für Theoretische Physik Parton Thermalization and Energy Loss in ultrarelativistic Heavy-Ion Collisions within a Parton Cascade Zhe Xu in collaboration with A. El, O.Fochler and C.Greiner QM2006, Shang Hai

  2. Motivation • fast thermalization • on-shell parton cascade Z. Xu and C. Greiner, PRC 71, 064901 (2005) • with only pQCD gg<->gg : no thermalization except with large s (AMPT,MPC) • including pQCD gg<->ggg: thermalization, hydro. behaviour and Jet-Quenching

  3. What is the correct quantity describing kinetic equilibration? • NOT the mean free path or collision rate ns • maybe nst with the transport cross section gg -> gg gg -> ggg B.Müller‘s question in Quark Matter 2005 One has to do detailed studies.

  4. momentum isotropization and kinetic equilibration Initial condition: Minijets p0=1.4 GeV

  5. q(t) gives the timescale of kinetic equilibration.

  6. Transport Rates Definition: Boltzmann equation

  7. The drift term is large.

  8. special case for isotropic distribution of collision angle

  9. Bremsstrahlung processes J.F.Gunion, G.F.Bertsch, Phys. Rev. D 25, 746(1982) LPM suppression: the formation time Bethe-Heitler regime

  10. Initial condition with Color Glass Condensate h: [-0.05:0.05] and xt < 1.5 fm

  11. Evolution of Particle Number in bottom-up scenario Andrej El • Particle number decreases rapidly in the very first moment • No net soft gluon production at early times!

  12. Jet-Quenching in a central Au Au collision at RHIC Oliver Fochler 3~4 too much

  13. elliptic flow in noncentral Au+Au collisions at RHIC: peripheral central

  14. Summary • PQCD Bremsstrahlung gg↔ggg are essential for the thermalization. • The transport rates are quantities determining the contribution of different processes to kinetic equilibration. • no bottom –up • large v2, but small RAA

  15. Minijets p0=1.4 GeV

  16. q(t)

  17. Simulation 1 Simulation 2 thermalization and hydrodynamical behavior NO thermalizationand free streaming Question: Why are gg<->ggg interactions essential for thermalization?

  18. 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:

  19. Initial conditions: minijets production with pt > p0 binary approximation  for a central Au+Au collision at RHIC at 200 AGeV using p0=2 GeV

  20. Initial conditions with smaller p0

  21. Kinetic and chemical equilibration in the central region: h: [-0.5:0.5] and xt < 1.5 fm 1~2 fm/c for the kinetic equilibration ~ 4 fm/c for the chemical equilibration

  22. Kinetic and chemical equilibration

  23. transverse energy at y=0 in Au+Au central collision

  24. Kinetic and chemical equilibration

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