A common description of jet-quenching and elliptic flow within a pQCD transport model

1. A common description of jet-quenching and elliptic flowwithin a pQCD transport model Oliver Fochler H-QM Graduate Day 18.06.2008 arXiv:0806.1169

2. present (near) future Oliver Fochler

3. Oliver Fochler

4. A perfect liquid? ideal hydro PRL 92, 052302 (2004) Universal bound from AdS/CFT? viscous hydro Oliver Fochler

5. Strong jet-quenching • nuclear modification factor relative to pp (binary collision scaling) • experiments show approx. factor 5 of suppression in hadron yields high energy particles as probes of the medium created in AA-collisions HP 2008, C. Vale Oliver Fochler

6. Some jet-quenching schemes • BDMPS (Baier, Dokshitzer, Mueller, Peigne, Schiff) • GLV (Gyulassy, Levai, Vitev) - opacity expansion • Djordjevic, Wicks, Horowitz, Adil.. • ASW (Armesto, Salgado, Wiedemann) - path integral in opacity • Dainese, Loizides, Paic, Eskola, Honkanen, Renk, Ruppert • AMY (Arnold, Moore, Yaffe) - finite temp. field theory • Qin, Turbide, Jeon, Gale, Ruppert • HT, Higher-Twist (Wang, Guo) - twist power expansion in DIS • Zhang, Zhang, Majumder, Fries, Mueller Oliver Fochler

7. Partonic transport model – BAMPS BAMPS=Boltzmann Approach to Multiple Particle Scattering, (Z. Xu, C. Greiner, Phys. Rev. C71) • microscopic transport simulations with full dynamics • attack various problems within one model (thermalization, RAA, jet tomography, v2, initial conditions,...) Oliver Fochler

8. matrix element integrated overmomentum space DV gg  gg gg  ggg Partonic transport model - BAMPS • LO pQCD cross sections • calculate transition probabilities for (test)particles within spatial cells • no geometric interpretation of cross sections • simulate gluon plasma including the processes • gggg cross section (in small-t (small angle) approximation) • transition probabilities Oliver Fochler

9. LPM-effect • possible interference effects • cannot be treated in quasi particle picture • incoherent treatment ofggggg processes • parent gluon must not scatter during formation time of emitted gluon • discard all possible interference effects (Bethe-Heitler regime) • obtain total cross section for ggggg via integration of the matrix element • Gunion-Bertsch matrix element Oliver Fochler

10. p1 p2 kt kt lab frame CM frame t = 1 / kt • total boost • integral cuts • b‘ << 1 (e.g. thermal particles): Reference frames for the LPM cut-off Oliver Fochler

11. Au+Au – Setup • central (b=0 fm) Au-Au collision at 200 AGeV • sampling of initial gluon plasma: • initial momentum distribution (mini-jets) according to • Glück-Reya-Vogt parameterization for structure functions; K = 2 • lower cut-off: p0 = 1.4 GeV (reproduces dET/dy) • particle production via standard nuclear geometry(Wood-Saxon density profile, Glauber-Model) • each parton is given a formation time • 35 testparticles • simulate evolution of fireball up to ~5 fm/c • when energy density in a cell drops below e=1 GeV • free streaming (in the respective cell) Oliver Fochler

12. Thermalization in Au+Au time evolution of pT spectra (central region, xT < 1.5 fm, |h| < 0.5) Oliver Fochler

13. Collective flow inelastic gluon interactions lead to sizeable v2 the shear viscosity can be computed v2 with fixded cs: cf. Molnar or AMPT Oliver Fochler

14. Energy loss in a static medium • gluon jet in a static, thermal medium of gluons • T = 400 MeV LPM cut-off increases due to boost Oliver Fochler

15. Au-Au – Nuclear modification factor • central (b=0 fm) Au-Au collision at 200 AGeV • initial distribution: mini-jets STAR: PRL 91, 172302 (2003) PHENIX: arxiv:0801.4020 (2008) Oliver Fochler

16. Au-Au – Nuclear modification factor • central (b=0 fm) Au-Au collision at 200 AGeV • initial distribution: mini-jets Oliver Fochler

17. Au-Au – Nuclear modification factor • central (b=0 fm) Au-Au collision at 200 AGeV • initial distribution: mini-jets Oliver Fochler

18. Fixed binary cross sections? Only binary collisions with fixed cross section 10 mb clearly overestimate jet-quenching! Oliver Fochler

19. Are we there yet? Well, not quite. Some things to look at.. Oliver Fochler HP 2008, C. Vale

20. More things to look at.. Oliver Fochler

21. In-Plane Out-of-Plane And more.. Oliver Fochler

22. And even more.. 3 < pt,trig< 4 GeV/c 4 < pt,trig < 6 GeV/c Oliver Fochler

23. Summary and to-do list • fully dynamic simulation of jet quenching in central Au+Au collision • thermalization, collective flow etc. are investigated in the same framework • quantitative description of v2 and RAA within a common description • not possible with binary collisions and fixed cross sections • include (light) quarks • implement fragmentation scheme • crank up computational performance (parallel computing?, testparticle scheme) • look at the observables from the previous slides.. Oliver Fochler

24. Thank you! Oliver Fochler

25. Mean transverse momentum • acquired mean transverse momentum squared per collision • divided by mean free path • T = 400 MeV Oliver Fochler

26. Energy loss in a static medium • gluon jet in a static, thermal medium of gluons • T = 400 MeV Oliver Fochler

27. Gluon-Quark-Ratio Oliver Fochler

28. Au-Au – Reconstruction • partons with high-pt too rare • simulate large number of initial conditions • select events according to highest pt-(test)particle • simulate only selected events and weight results Oliver Fochler full: 200000 events; reconstruction: 40 events per pt-bin, ~1000 total