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Hot QCD Matter: An Experimenter’s Dream and Nightmare

Hot QCD Matter: An Experimenter’s Dream and Nightmare. B. Jacak Stony Brook October 25, 2009. Hot QCD Matter. Exciting and surprising results from RHIC What IS the coupling in the plasma? What are the degrees of freedom - point particles? pure fields? composite quasiparticles?

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Hot QCD Matter: An Experimenter’s Dream and Nightmare

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  1. Hot QCD Matter: An Experimenter’s Dream and Nightmare B. Jacak Stony Brook October 25, 2009

  2. Hot QCD Matter • Exciting and surprising results from RHIC • What IS the coupling in the plasma? • What are the degrees of freedom - point particles? pure fields? composite quasiparticles? • What are the physical properties of the plasma? • Thermal: T,, EOS • opacity, fluidity • Dynamic: viscosity, diffusion, energy transport • color screening, correlations inside • Measure the above in a system lasting <10 fm/c! • Nature does the time integral, whether we like it or not

  3. Today (results from PHENIX) • Exciting and surprising results from RHIC • What IS the coupling in the plasma? • What are the degrees of freedom - point particles? pure fields? composite quasiparticles? • What are the physical properties of the plasma? • Thermal: T,, EOS • opacity, fluidity • Dynamic: viscosity, diffusion, energy transport • color screening, correlations inside • Measure the above in a system lasting <10 fm/c! • Nature does the time integral, whether we like it or not

  4. 4 Initial State Temperature: direct photons Low mass, high pT e+e- nearly real photons Large enhancement above p+p in the thermal region arXiv:0804.4168v1 [nucl-ex] • Exponential fit in pT: Tavg = 221 ±23 ±18 MeV • Multiple hydro models reproduce data • Tinit ≥ 300 MeV

  5. Lepton pair emission  EM correlator Medium modification of meson Chiral restoration Hadronic contribution Vector Meson Dominance q qq annihilation Thermal radiation from partonic phase (QGP) q e.g. Rapp, Wambach Adv.Nucl.Phys 25 (2000) Emission rate of dilepton per volume g*ee decay Boltzmann factor temperature EM correlator Medium property From emission rate of dilepton, the medium effect on the EM correlator as well as temperature of the medium can be decoded. Yasuyuki Akiba - PHENIX QM09

  6. Dilepton emission Calculation: R. Rapp Prob. g*l+l- Dilepton y=0, pt=1.025 GeV/c virtual photon Vacuum EM correlator Hadronic Many Body theory Dropping Mass Scenario q+q annihilation (HTL improved) (q+gq+gqee not shown) Normally: dilepton emission as spectrum dN/dpTdM. Mass spectrum at low pT is distorted by virtual photonee decay factor 1/M: steep rise as M0 qq annihilation contribution negligible at low mass due to m**2 factor of the EM correlator NB: calculation omits partonic photon emission process q+gq+gq+e+e-

  7. Relation of dileptons and virtual photons Yasuyuki Akiba - PHENIX QM09 Emission rate of dilepton per volume Emission rate of (virtual) photon per volume Prob. g*l+l- Relation between them This relation holds for the yield after space-time integral Dilepton virtual photon Virtual photon emission rate can be determined from dilepton emission rate M x dNee/dM gives Virtual photon yield For M0, ng*  ng(real) so real photon emission rate can also be determined

  8. Virtual photon emission rate Vaccuum EM correlator Hadronic Many Body theory Dropping Mass Scenario q+q annihilaiton (HTL improved) (q+gq+gqee not shown) Prob. g*l+l- Dilepton virtual photon at y=0, pt=1.025 GeV/c Same calculation shown as virtual photon emission rate. Note: steep rise at M=0 is gone, and the virtual photon emission rate is more directly related to the underlying EM correlator. For M0, ng*  ng(real) q+gq+g* is not shown; is similar to HMBT at this pT

  9. Excess of virtual photon Excess over cocktail ~ constant with mass at high pT. Convert to virtual photon yield by 1/M factor from the virtual photon decay.  distribution is ~flat over 0.5 GeV/c2 Extrapolation to M=0 should give the real photon emission rate. No indication of strong modification of EM correlator at high pT ! presumably the virtual photon emission is dominated by processes e.g. p+rp+g* or q+gq+g* Excess*M (A.U). Yasuyuki Akiba - PHENIX QM09

  10. 0 < pT < 8 GeV/c 0 < pT < 0.7 GeV/c 1.5 < pT < 8 GeV/c 0.7 < pT < 1.5 GeV/c NEW DATA COMING IN 2010 How about low pT ? Excess*M (A.U). Low pT shape incompatible with constant virtual photon emission rate… Enhancement of EM correlator at low mass, low pT? NEED HELP FROM THEORY!!

  11. Interactions within the plasma • Experimentalist’s simple minded picture • Strong coupling = • interactions among multiple neighbors • Of course this must cause correlations within plasma • also increases opacity • how is the energy loss mechanism affected? • is the quark gluon plasma “black”?

  12. Iconic jet quenching (opacity) result

  13. Insights somewhat unsatisfying S. Bass, et al. Phys.Rev.C79:024901,2009 Put 3 different energy loss schemes into common, realistic hydrodynamic calculation

  14. We can do better! • Extend the pT range • Difficult for 0 because • decay g’s merge in the • calorimeter • Measuring h instead of • p0 is the solution RAA remains flat to at least 22 GeV/c!

  15. Next step: constrain geometry: high-pT v2 arXiv:0903.4886 (Run-4 data)

  16. in-plane intermediate out-of-plane Out-of-plane vs. in-plane pT Run-7 RAA NPart • Out-of plane RAA nearly flat with centrality at low pT • In- and out-of-plane converge at high-pT (~10GeV/c) Carla Vale - PHENIX QM09

  17. Differentiate among energy loss models! Calculations by S.Bass et al in arXiv:0808.0908 Carla Vale - PHENIX QM09

  18. Penetrating production Tangential production in-plane in-plane π π out-plane out-plane PTY = per-trigger yield π π Away PTY Away PTY π 0 φs φs 0 π More differential yet: dijet reaction plane dependence

  19. Medium is not totally opaque Away side yield Away side yields drop from in-plane to out-of-plane: jets do penetrate medium

  20. 3<pt,trigger<4 GeV pt,assoc.>2 GeV Au+Au 0-10% preliminary STAR Shocks? Medium spectrum Harder than inclusive, softer than jet p+p central Au+Au

  21. Jet-medium interaction Centrality: 40-45% jet medium Central: 5-10% medium Jet suppressed

  22. -jet (-h) correlation: calibrated probe fragmentation of  tagged jets in/out of medium p+p slope: 6.89  0.64 Au+Au slope: 9.49  1.37 Challenge: understand energy transfer to/from the medium! Coupling properties…

  23. Next step: full jet reconstruction Gaussian filter algorithm optimize signal/background by focusing on jet core stabilizes jet axis in presence of background

  24. In ion collisions life is tougher signal background

  25.  s Yikes! RAA flat to > 30 GeV/c pT In Cu+Cu

  26. Non photonic electrons 0,  PRELIM. minimum-bias Rapp & van Hees, PRC 71, 034907 (2005) Run-7 Run-4 Heavy quark energy loss (large!) Who ordered that? Mix of radiation + collisions (diffusion) but collisions with what? AdS/CFT provides an answer, but…

  27. Not all energy loss is created equal!

  28. High meff  large collisional energy loss R. Kolevatov & U.A. Wiedemann arXiV:0812.0270 • The “clumps”? • b/c separation allows to test!

  29. Upgrades over next ~3 years PHENIX Upgrades Forward Calorimeter  at = 1-3 Correlate with mid-y h± Silicon VTX, FVTX Tag displaced vertex for heavy quark decays Track charged hadrons in large acceptance *In addition to RHIC-II luminosity upgrade x8

  30. Over next decade: entirely new questions • Precision jet probes of energy transport in medium • What degrees of freedom? • Heavy quark fragmentation modified? • Theory + dynamics: qualitative  quantitative • What is the screening length in strongly coupled QCD matter? • Experiment: onium spectroscopy in pp, dAu, AuAu • Theory: understand production & cold matter effects Supplement silicon tracker to enhance momentum resolution Enhance electron ID capabilities inner barrel compact calorimeter?

  31. HAPPY BIRTHDAY Conclusion: • It could be that theorists’ dreams make for the experimenters’ nightmares… • The really interesting stuff is hard to measure • Experimenters’ dream results are definitely the stuff of the theorists’ nightmares • We really want to pin you down • Extract properties of hot QCD matter by constraining theory + phenomenology with data! • But for Al - we wish very sweet dreams! • We’ll work hard for those sugarplums

  32. backup slides

  33. Tag jet energy with direct photon M. McCumber WWND ‘09

  34. Local Slopes of Inclusive mT Spectra Data have soft mT component not expected from hadron decays Note: Local slope of all sources! need more detailed analysis Tdata ~ 240 MeV • Tdata ~ 120 MeV Soft component below mT ~ 500 MeV: Teff < 120MeV independent of mass more than 50% of yield Axel Drees 34

  35. 35 Open Heavy Flavor •  determined three different ways: • single electron spectra methods: • cocktail subtraction • converter • di-electrons • Muon measurement at forward rapidity is consistent dheavy/dy (mb) Mike Leitch - PHENIX QM09

  36. b + c ! b quarks and medium effects… e-h correlations to tag D vs. B decays B meson spectra Oh oh!

  37. 37/12 Nuclear Effects Should modify low pT direct g yield → Evaluate using d+Au data. • Systematic errors on Run3 d+Au results are still large. • At 2-3 GeV/c, data looks in agreement with pQCD calculation. • → No modification of direct g yield by nuclear effects? • Run 8 analysis underway: x30 statistics 04/02/2009 Quark Matter '09 Y. Yamaguchi

  38. Both ridge & shoulder yields grow

  39. Shoulder and ridge have the same physics! See also Rudy Hwa, Jiangyong Jia recent talks Away/near to ~ cancel acceptance

  40. From the bulk or jet-like? arXiv:0712.3033 pT spectra Particle content PHENIX PRL 101, 082301 (2008) arXiv:0712.3033 Answer: it’s more like the bulk! QGP-like

  41. Are shocks in strongly coupled EM plasma. So sQGP could also support shockwaves (shear generally a phenomenon in crystals but not liquids)

  42. In the most central collisions

  43. v2 pT (GeV/c) Quantifying the viscosity Need: • 3-d viscous hydro calculations • Precision data • Mass dependence of v2 + other observables for pT transport Romatschke & Romatschke, arXiv:0706.1522 PHENIX Preliminary /s ~ 0 - 0.8 Recall: in ideal hydro mfp=0 Conjectured /s bound: 1/4 Work is underway to control: initial state geometry gluon distribution

  44. e+ Gluon Compton g* e- q g q Direct g*/Inclusive g*determined by fitting each pT bin p+p Au+Au (MB) r : direct g*/inclusive g* Dileptons at low mass and high pT 1 < pT < 2 GeV 2 < pT < 3 GeV 3 < pT < 4 GeV 4 < pT < 5 GeV PHENIX Preliminary PHENIX Preliminary • m<2p only Dalitz contributions • p+p: no enhancement • Au+Au: large enhancement at low pT • A real g source  • virtualg with v. low mass • We assume internal conversion of direct photon  extract the fraction of direct photon

  45. for low mass, pT > 1 GeV/c direct * fraction of inclusive * (mostly ,) is  real  fraction of  (mostly , ) hadron cocktail mee direct photons via e+e- low mass and pT >> mee dominated by decay of *

  46. Virtual Photon Measurement • Any source of real g can emit g* with very low mass. • Relation between the g* yield and real photon yield is known. Eq. (1) S : Process dependent factor • Case of Hadrons • Obviously S = 0 at Mee > Mhadron • Case of direct g* • If pT2>>Mee2 • Possible to separate hadron decay components from real signal in the proper mass window.

  47. Where does the lost energy go? • Radiated particles still correlated • with the jet • Completely absorbed by plasma • Thermalized? • Collective conservation of momentum? • Excites collective response in plasma • Shocks or sound waves? • Wakes in the plasma?

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