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production @. Ro. Robert Pak. f or PHENIX Collaboration. Knobs to turn: Centrality, N part Collision energy, √ s NN In-medium path length, L, using event plane Observables: x T scaling of invariant yield Nuclear modification factor, R AA Fractional momentum loss, S loss

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  1. production@ Ro Robert Pak for PHENIX Collaboration WWND 2013

  2. Knobs to turn: • Centrality, Npart • Collision energy, √sNN • In-medium path length, L, using event plane • Observables: • xT scaling of invariant yield • Nuclear modification factor, RAA • Fractional momentum loss, Sloss • Elliptical flow, v2 • Model comparisons • Summary • Acknowledgements WWND 2013

  3. p0 invariant mass PRC 80, 054907 (2009) WWND 2013

  4. h-meson to p0 ratio arXiv:1208.2254v2 • For constant fit to min. bias data: h/p0 = 0.45 +/- 0.01 • Similar to d+Au (0.47 +/- 0.03) and p+p (0.48 +/- 0.03) • Lack of nuclear effects at high pT indicates fragmentation occurs outside the medium WWND 2013

  5. p0invariant yields PRL 101, 232301 (2008) WWND 2013

  6. xT= 2pT/√s scaling In hard scattering region: universal scaling function For isolated photons from p+p collisions in Bjorken’sparton model: neff= constant = 4.0 PRD 86, 072008 (2012) WWND 2013

  7. xT scaling (cont) PRL 109, 152301 (2012) • In pQCDcontributions from: • running as(Q2) • PDF(and FF) evolution • Other effects: • kTsmearing • higher-twist phenomena So neffnot constant, rather: to compare different beam energies. Largest deviation for 39 and 200 GeVAu+Au comparison hard scattering not dominant source of high pTp0 in 39 GeVAu+Aucollisions WWND 2013

  8. nuclear modification factor - RAA PRL 101, 162301 (2008) n.b., RAA requires p+p reference data at corresponding √s. WWND 2013

  9. q̂ from PQM Early attempt to extract transport coefficient q̂ using a parton quenching model PRC 77, 064907 (2008) WWND 2013

  10. more recent p0invariant yields arXiv:1208.2254v2 WWND 2013

  11. RAA @ 200 GeV arXiv:1208.2254v2 WWND 2013

  12. fit the data Above Npart = 167 slope of linear fit is significantly different from zero WWND 2013

  13. cf., ALICE • Similar suppression for 14x increase in colliding energy at LHC ~2x increase in parton density at LHC • Slope in PHENIX data comes as no surprise arXiv:1208.2711v1 WWND 2013

  14. fractional momentum shift arXiv:1208.2254v2 PRL 109, 152301 (2012) Partons in 200 GeV collisions suffer largest average momentum loss WWND 2013

  15. Sloss(= dpT/pT) vs. centrality WWND 2013

  16. Sloss@ PHENIX, cf., ALICE arXiv:1208.2254v2 WWND 2013

  17. model comparisons • AMY: Arnold, Moore & Yaffe, • JHEP 0206, 030 (2006) • HT: X.N. Wang & X. Guo, • NPA 696, 788 (2001) • ASW: Salgado & Wiedemann, • PRD 68, 014008 (2003) • Parton energy loss models incorporated into same 3D hydro calculation • No distinguishing power despite differences in q̂ WWND 2013

  18. pseudorapidity WWND 2013

  19. spectators flow participants • More recently, generalized eccentricities for higher flow moments: • Measured values must be corrected by event plane resolution: WWND 2013

  20. RAA vs. event plane arXiv:1208.2254v2 WWND 2013

  21. centrality dependence 3.4 fm • Suppression increases with centrality • In-plane suppression less than out-of-plane • Average path length in medium changes more in-plane than out-of-plane difference in RAA becomes larger as centrality decreases • All in agreement with: • PRC 80, 054907 (2009) 5.9 fm 6.1 fm 6.7 fm WWND 2013

  22. RAA vs. event plane, cf., hydro models Greater sensitivity in-plane: arXiv:1208.2254v2 cubic L dependence WWND 2013

  23. in-medium path length dependence PRL 105, 142301 (2010) WWND 2013

  24. more hydro comparisons Majumder & C.Shen PRL 109, 202301 (2012) Progress extracting q̂for comparison to LHC WWND 2013

  25. √sNN dependence of PID v2 preliminary preliminary same mass scaling pattern as seen in 200 GeVAu+Au collisions baryons PRL 98, 162301 (2007) mesons WWND 2013

  26. PID v2/nq quark number (nq) scaling indicates partonic collective flow down to 39 GeV preliminary preliminary baryons mesons Phys. Rev. Lett. 98, 162301 (2007) WWND 2013

  27. more recent PID v2 PRC 85, 064914 (2012) • New TOF patch installed to extend PID • quark number scaling breaks down at higher pT Au+Au√sNN = 200 GeV WWND 2013

  28. Summary • Onset of hard processes at high pT from xT scaling • Onset of suppression from RAAvs √sNN • PHENIX data provides a bridge to RAA @ LHC • Sloss(= dpT/pT) increases with Npartand √sNN • In-medium path length dependence > L2 for parton energy loss • Progress to extract q̂ through model comparisons • From PID collective flow in Au+Au collisions: • partonic flow (with perfect fluidity) down to 39 GeV • quark number scaling breaks down at higher pT WWND 2013

  29. WWND 2013

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