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QCD Matter Thermalization at RHIC and LHC

SQM 2008, Beijing, China, Oct. 9. QCD Matter Thermalization at RHIC and LHC. Zhe Xu. with L.Cheng, A. El, K. Gallmeister and C. Greiner. Motivation and Summary. P.Huovinen et al., PLB 503, 58 (2001). Assumption: full thermalization at 0.6 fm/c. From transport calculations using BAMPS

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QCD Matter Thermalization at RHIC and LHC

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  1. SQM 2008, Beijing, China, Oct. 9 QCD Matter Thermalization at RHIC and LHC Zhe Xu with L.Cheng, A. El, K. Gallmeister and C. Greiner

  2. Motivation and Summary P.Huovinen et al., PLB 503, 58 (2001) Assumption: full thermalization at 0.6 fm/c From transport calculations using BAMPS • Fast Thermalization from pQCD: 2-3 important equilibration time: teq=1 fm/c • Elliptic flow v2:high in 2-3 Viscosity: small ~ 0.08-0.16 Zhe Xu, Beijing, SQM 2008

  3. Outline • Transport model • Why 2-3 important • Initial condition dependence of • thermalization at RHIC and LHC • Summary Zhe Xu, Beijing, SQM 2008

  4. Transport Model BAMPS: BoltzmannApproachofMultiPartonScatterings A transport algorithm solving the Boltzmann-Equations for on-shell partons with pQCD interactions new development ggg gg (Z)MPC, VNI/BMS, AMPT, PACIAE Elastic scatterings are ineffective in thermalization ! Inelastic interactions are needed ! Zhe Xu, Beijing, SQM 2008

  5. Stochastic algorithm P.Danielewicz, G.F.Bertsch, Nucl. Phys. A 533, 712(1991) A.Lang et al., J. Comp. Phys. 106, 391(1993) Space has to be divided into small cells ! D3x collision rate per unit phase space for incoming particles p1 and p2 with D3p1 and D3p2: collision probability (Monte Carlo) Zhe Xu, Beijing, SQM 2008

  6. Interaction Probability ZX and C. Greiner,PRC 71, 064901 (2005) Zhe Xu, Beijing, SQM 2008

  7. screened partonic interactions in leading order pQCD J.F.Gunion, G.F.Bertsch, PRD 25, 746(1982) T.S.Biro at el., PRC 48, 1275 (1993) S.M.Wong, NPA 607, 442 (1996) screening mass: LPMsuppression: the formation time Lg: mean free path Zhe Xu, Beijing, SQM 2008

  8. distribution of collision angles at RHIC energies gg gg: small-angle scatterings gg ggg: large-angle bremsstrahlung Zhe Xu, Beijing, SQM 2008

  9. Transport Rates ZX and C. Greiner, PRC 76, 024911 (2007) • Transport rate is the correct quantity describing kinetic • equilibration. • Transport collision rates have an indirect relationship • to the collision-angle distribution. Zhe Xu, Beijing, SQM 2008

  10. Transport Rates for a static gluon gas Large Effect of 2-3 ! Zhe Xu, Beijing, SQM 2008 ZX and C.Greiner, PRL 100, 172301, 2008

  11. time scale of thermalization in heavy ion collisions at collision center: xT<1.5 fm, |h| < 0.2 of a central Au+Au at s1/2=200 GeV Initial conditions: minijets pT>1.4 GeV; coupling as=0.3 theoretical result from parton cascade calculations teq = time scale of kinetic equilibration. Zhe Xu, Beijing, SQM 2008

  12. Elliptic Flow and Shear Viscosity in 2-3 at RHIC 2-3Parton cascade BAMPS ZX, Greiner, Stöcker, PRL 101, 082302, 2008 viscous hydro. Romatschke, PRL 99, 172301,2007 h/s at RHIC > 0.08 Zhe Xu, Beijing, SQM 2008

  13. ZX, C.Greiner, H. Stöcker, PRL 101:082302,2008 • Perturbation QCD describes well • fast thermalization, • low h/s, • large v2 at RHIC. Zhe Xu, Beijing, SQM 2008

  14. Initial Condition – Wounded Nucleons P+P using PYTHIA 6.4 semi-hard partonic collisions with initial and final radiations string breaking by L.Cheng Zhe Xu, Beijing, SQM 2008

  15. Initial Condition – Color Glass Condensate Kharzeev, Levin, Nardi, NPA 730, 448 (2004); 747, 609 (2005) Hirano and Nara, NPA 743, 305 (2004) Adil, Drescher, Dumitru, Hayashigaki, Nara, PRC 74, 044905 (2006) Zhe Xu, Beijing, SQM 2008

  16. Wounded nucleons vs Color Glass Condensate by L.Cheng and A. El Initial Conditions: • Only gluons from WN • Gluons and quarks from WN. Quarks as gluons. • Color Glass condensate Formation time: 0.15 fm/c Zhe Xu, Beijing, SQM 2008

  17. Decrease of the transverse energy using BAMPS QGP from wn has a larger h/s than 0.15. QGP from cgc has a smallerh/s than 0.15. Zhe Xu, Beijing, SQM 2008

  18. Kinetic equilibration no difference between wn and cgc ! Zhe Xu, Beijing, SQM 2008

  19. Chemical equilibration due to gg <-> ggg wn: gluons system stays in chemical equilibrium. cgc: chemical equilibrium is achieved at the same timesacle, 1.5 fm/c, as the kinetic equilibration. Zhe Xu, Beijing, SQM 2008

  20. Initial conditions at LHC by L.Cheng and A. El Gluons dominante the initial conditions. Initial Conditions: • Gluons and quarks from WN, Quarks as gluons • Color Glass condensate Formation time: 0.15 fm/c Zhe Xu, Beijing, SQM 2008

  21. Prediction of final dET/dy at LHC 2150 GeV 1620 GeV Zhe Xu, Beijing, SQM 2008

  22. Thermal equilibration at LHC no difference between wn and cgc time scale of kinetic equilibration: 0.8 ~ 1.6 fm/c initial difference between wn and cgc time scale of chemical equilibration: 1.5 fm/c Zhe Xu, Beijing, SQM 2008

  23. Summary Inelastic pQCD interactions (23 + 32) explain: • Fast Thermalization • Large Collective Flow • Small shear Viscosity of QCD matter at RHIC Wounded nucleons vs. CGC • wn: smaller dET/dy -> smaller h/s cgc: larger dET/dy -> larger h/s • same kinetic equil., different chemical equil. Zhe Xu, Beijing, SQM 2008

  24. more details on elliptic flow at RHIC … moderate dependence on critical energy density h/s at RHIC: 0.08-0.2 Zhe Xu, Beijing, SQM 2008

  25. … looking on transverse momentum distributions gluons are not simply pions …need hadronization (and models) to understand the particle spectra Zhe Xu, Beijing, SQM 2008

  26. Life time of QGP Tc=175 MeV Zhe Xu, Beijing, SQM 2008

  27. Zhe Xu, Beijing, SQM 2008

  28. Comparisons with 1+1 Bjorken Zhe Xu, Beijing, SQM 2008

  29. pt-spectra Zhe Xu, Beijing, SQM 2008

  30. pT spectra at collision center: xT<1.5 fm, Dz < 0.4 t fm of a central Au+Au at s1/2=200 GeV Initial conditions: minijets pT>1.4 GeV; coupling as=0.3 simulation pQCD 2-2 + 2-3 + 3-2 simulation pQCD, only 2-2 3-2 + 2-3: thermalization! Hydrodynamic behavior! 2-2: NOthermalization Zhe Xu, Beijing, SQM 2008

  31. What determines the equilibration time scale t ? Cross section doesnotdetermine t! ZX and C.Greiner, arXiv: 0710.5719 [nucl-th] Zhe Xu, Beijing, SQM 2008

  32. BUT, this isnotthefull story ! Zhe Xu, Beijing, SQM 2008

  33. From Navier-Stokes approximation From Boltzmann-Eq. relation between h and Rtr Zhe Xu, Beijing, SQM 2008

  34. Ratio of shear viscosity to entropy density in 2-3 AdS/CFT RHIC Zhe Xu, Beijing, SQM 2008

  35. Zhe Xu, Beijing, SQM 2008

  36. total transverse energy per rapidity at midrapidity Zhe Xu, Beijing, SQM 2008

  37. Initial conditions Glauber-type: Woods-Saxon profile, binary nucleon-nucleon collision minijets production with pt > p0 for a central Au+Au collision at RHIC at 200 AGeV using p0=1.4 GeV Zhe Xu, Beijing, SQM 2008

  38. The drift term is large. gg<->ggg interactions are essential for kinetic equilibration! Zhe Xu, Beijing, SQM 2008

  39. due to the fact that a 2->3 process brings one more particle toward isotropy than a gg->gg process. Zhe Xu, Beijing, SQM 2008

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