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

2 Hot QCD Matter l 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? l What are the physical properties of the plasma? Thermal: T, , EOS opacity, fluidity Dynamic: viscosity, diffusion, energy transport color screening, correlations inside l 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) l 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? l What are the physical properties of the plasma? T Thermal: T, , EOS opacity opacity, fluidity energy transport Dynamic: viscosity, diffusion, energy transport color screening, correlations inside l Measure the above in a system lasting <10 fm/c! Nature does the time integral, whether we like it or not

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

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

6 Dilepton emission Vacuum EM correlator Hadronic Many Body theory Dropping Mass Scenario q+q annihilation (HTL improved) (q+g  q+   qee not shown) Calculation: R. Rapp y=0, pt=1.025 GeV/c Normally: dilepton emission as spectrum dN/dp T dM. Mass spectrum at low p T 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+   q+e + e - Dilepton virtual photon Prob.  *  l + l -

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

8 Virtual photon emission rate at y=0, pt=1.025 GeV/c Vaccuum EM correlator Hadronic Many Body theory Dropping Mass Scenario q+q annihilaiton (HTL improved) (q+g  q+   qee not shown) 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, n  *  n  (real) q+g  q+  * is not shown; is similar to HMBT at this p T Dilepton virtual photon Prob.  *  l + l -

9 Excess of virtual photon Excess over cocktail ~ constant with mass at high p T. Convert to virtual photon yield by 1/M factor from the virtual photon decay.  distribution is ~flat over 0.5 GeV/c 2 Extrapolation to M=0 should give the real photon emission rate. No indication of strong modification of EM correlator at high p T ! presumably the virtual photon emission is dominated by processes e.g.  +    +  * or q+g  q+  * Excess*M (A.U). Yasuyuki Akiba - PHENIX QM09

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

11 Interactions within the plasma l Experimentalist’s simple minded picture Strong coupling = interactions among multiple neighbors l 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! l Extend the p T range Difficult for  0 because decay  ’s merge in the calorimeter Measuring  instead of  0 is the solution R AA remains flat to at least 22 GeV/c!

15 Next step: constrain geometry: high-p T v 2 arXiv: (Run-4 data)

16 pTpT N Part R AA Out-of plane R AA nearly flat with centrality at low p T In- and out-of-plane converge at high-p T (~10GeV/c) Out-of-plane vs. in-plane in-plane intermediat e out-of- plane Carla Vale - PHENIX QM09 Run-7

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

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

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

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

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

22  -jet (  -h) correlation: calibrated probe p+p slope: 6.89  0.64 Au+Au slope: 9.49  1.37 fragmentation of  tagged jets in/out of medium 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 In Cu+Cu Yikes! R AA flat to > 30 GeV/c p T   

26 Heavy quark energy loss (large!) PRELIM. Run-4 Run-7 Rapp & van Hees, PRC 71, (2005) minimum-bias Non photonic electrons  0,  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 m eff  large collisional energy loss R. Kolevatov & U.A. Wiedemann arXiV: lTlThe “clumps”? lblb/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 l Precision jet probes of energy transport in medium What degrees of freedom? Heavy quark fragmentation modified? Theory + dynamics: qualitative  quantitative l 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 Conclusion: l It could be that theorists’ dreams make for the experimenters’ nightmares… The really interesting stuff is hard to measure l 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! l But for Al - we wish very sweet dreams! We’ll work hard for those sugarplums HAPPY BIRTHDAY

32 l backup slides

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

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

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

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

37 04/02/2009Quark Matter '09 Y. Yamaguchi Should modify low p T direct  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  yield by nuclear effects?  Run 8 analysis underway: x30 statistics 37/12 Nuclear Effects

38 Both ridge & shoulder yields grow

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

40 From the bulk or jet-like? arXiv: Answer: it’s more like the bulk!  QGP-like PHENIX PRL 101, (2008) p T spectra Particle content

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

42

43 In the most central collisions

44 Quantifying the viscosity Need: 3-d viscous hydro calculations Precision data Mass dependence of v 2 + other observables for p T transport p T (GeV/c) v2v2  /s ~ Recall: in ideal hydro mfp =0 Conjectured  /s bound: 1/4  Work is underway to control: initial state geometry gluon distribution Romatschke & Romatschke, arXiv: PHENIX Preliminary

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

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

47 Virtual Photon Measurement  Case of Hadrons Obviously S = 0 at M ee > M hadron  Case of direct  * – If p T 2 >>M ee 2  Possible to separate hadron decay components from real signal in the proper mass window.  Any source of real  can emit  * with very low mass.  Relation between the  * yield and real photon yield is known. S : Process dependent factor Eq. (1)

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