1. 1 Properties of the sQGP measured with STAR Rene Bellwied Wayne State University XLV International Winter Meeting on Nuclear Physics, BORMIO 2007, Jan.13 th -20 th

2. 2 Did we serve up the perfect liquid ? (The AIP Science Story of 2005) “The truly stunning finding at RHIC that the new state of matter created in the collisions of gold ions is more like a liquid than a gas gives us a profound insight into the earliest moments of the universe. The possibility of a connection between string theory, cosmology and RHIC collisions is unexpected and exhilarating. It may well have a profound impact on the physics of the twenty-first century.” Dr. Raymond L. Orbach Director of the DOE Office of Science.

3. 3 microexplosionsfemtoexplosions ss0.1  J 1  J  10 17 J/m 3 5 GeV/fm 3 = 10 36 J/m 3 T10 6 K200 MeV = 10 12 K rate10 18 K/s10 35 K/s

4. 4 Major discoveries in AuAu collisions ‘The Big Three’ (leading to the discovery of the sQGP = the Perfect Quark Gluon Liquid)

5. 5 STAR, nucl-ex/0305015 energy loss pQCD + Shadowing + Cronin pQCD + Shadowing + Cronin + Energy Loss # I: The medium is dense and partonic Deduced initial gluon density at   = 0.2 fm/c dN glue /dy ≈ 800-1200  ≈ 15 GeV/fm 3, eloss = 15*cold nuclear matter (compared to HERMES eA or RHIC dA) (e.g. X.N. Wang nucl-th/0307036) ?

6. 6 # II: The medium behaves like a liquid x y z Strong collective flow: elliptic and radial expansion with mass ordering requires partonic hydrodynamics: strong coupling, small mean free path, lots of interactions NOT plasma-like more like a perfect liquid (near zero viscosity, d.o.f. ?)

7. 7 # III: The medium consists of constituent quarks ? baryons mesons

8. 8 Consequences of a perfect liquid All “realistic” hydrodynamic calculations for RHIC fluids to date have assumed zero viscosity  = 0  “perfect fluid” –But there is a (conjectured) quantum limit –Where do “ordinary” fluids sit wrt this limit? –RHIC “fluid” might be at ~2-3 on this scale (!) 400 times less viscous than water, 10 times less viscous than superfluid helium ! T=10 12 K Motivated by calculation of lower viscosity bound in black hole via supersymmetric N=4 Yang Mills theory in AdS (Anti deSitter) space (conformal field theory)

9. 9 Viscosity in Collisions Viscosity in Collisions Hirano & Gyulassy, Teaney, Moore, Yaffe, Gavin, etc. supersymmetric Yang-Mills:  s   pQCD and hadron gas:  s ~ 1 liquid ? liquid plasma gas d.o.f. in perfect liquid ? Bound states ?, constituent quarks ?, heavy resonances ?

10. 10 Suggested Reading Suggested Reading November, 2005 issue of Scientific American “The Illusion of Gravity” by J. Maldacena A test of this prediction comes from the Relativistic Heavy Ion Collider (RHIC) at BrookhavenNational Laboratory, which has been colliding gold nuclei at very high energies. A preliminary analysis of these experiments indicates the collisions are creating a fluid with very low viscosity. Even though Son and his co-workers studied a simplified version of chromodynamics, they seem to have come up with a property that is shared by the real world. Does this mean that RHIC is creating small five-dimensional black holes? It is really too early to tell, both experimentally and theoretically. (Even if so, there is nothing to fear from these tiny black holes-they evaporate almost as fast as they are formed, and they "live" in five dimensions, not in our own four- dimensional world.)

11. 11 A few introductory remarks At RHIC we found strongly coupled partonic, collective matter (sQGP). The discovery phase has been concluded. The characterization phase is just beginning. What do we need to know ? LET’S BE QUANTITATIVE: –Let’s determine the viscosity bound at RHIC –Let’s determine the energy loss characteristics in the dense medium –Let’s determine the medium response to the energy loss –Let’s determine the degrees of freedom in the liquid phase

12. 12 Characterization I: flow, viscosity

13. 13 A new picture of an old idea, energy dependence of applicability of ideal hydrodynamics Consistent v 2 /  scaling for all energies and collision systems.

14. 14 χ 2 minimum result D->e 2σ 4σ 1σ Even charm flows strong elliptic flow of electrons from D meson decays → v 2 D > 0 v 2 c of charm quarks? recombination Ansatz: (Lin & Molnar, PRC 68 (2003) 044901) universal v 2 (p T ) for all quarks simultaneous fit to , K, e v 2 (p T ) a = 1 b = 0.96  2 /ndf: 22/27 within recombination model: charm flows like light quarks!

15. 15 How can a heavy quark flow like the light quarks ? Many interactions of the heavy quark in the partonic phase (thermalization ?) Ideal hydro - low viscosity, high Diffusion What are the degrees of freedom ? : dressed up constituent quarks, bare heavy quarks, gluons, colorless bound states (glueballs ?), quasi-D’s (isotropic elastic parton scattering (Rapp / van Hees, this workshop)). Let’s measure v 2 for D (through hadron channels), B-mesons (through J/  channels  and onium states.

16. 16 Characterization II: heavy flavor energy loss

17. 17 An important detail: the medium is not totally opaque There are specific differences to the flavor of the probe Theory: there are two types of e-loss: radiative and collisional, plus dead-cone effect for heavy quarks Flavor dependencies map out the process of in-medium modification Experiment: there are baryon/meson differences

18. 18 BUT: heavy quarks show same e-loss than light quarks R AA of electrons from heavy flavor decay Describing the suppression is difficult for models radiative energy loss with typical gluon densities is not enough (Djordjevic et al., PLB 632(2006)81) models involving a very opaque medium agree better (qhat very high !!) (Armesto et al., PLB 637(2006)362) collisional energy loss / resonant elastic scattering (Wicks et al., nucl-th/0512076, van Hees & Rapp, PRC 73(2006)034913) heavy quark fragmentation and dissociation in the medium → strong suppression for charm and bottom (Adil & Vitev, hep-ph/0611109)

19. 19 Constraining medium viscosity  /s Simultaneous description of STAR R(AA) and PHENIX v2 for charm. (Rapp & Van Hees, PRC 71, 2005) Ads/CFT ==  /s ~ 1/4  ~ 0.08 Perturbative calculation of D (2  t) ~6 (Teaney & Moore, PRC 71, 2005) ==  /s~1 transport models require –small heavy quark relaxation time –small diffusion coefficient D HQ x (2  T) ~ 4-6 –this value constrains the ratio viscosity/entropy  /s ~ (1.3 – 2) / 4  within a factor 2 of conjectured lower quantum bound consistent with light hadron v 2 analysis electron R AA ~  0 R AA at high p T - is bottom suppressed as well?

20. 20 An alternate idea (Abdel-Aziz & Gavin) viscous liquid pQGP ~ HRG ~ 1 fm nearly perfect sQGP ~ (4  T c ) -1 ~ 0.1 fm Abdel-Aziz & S.G Level of viscosity will affect the diffusion of momentum correlations kinematic viscosity effect on momentum diffusion: limiting cases: wanted: rapidity dependence of momentum correlation function Broadening from viscosity QGP + mixed phase + hadrons  T(  )  = width of momentum covariance C in rapidity

21. 21 we want: STAR measurement STAR measures: maybe  n  2  * STAR, PRC 66, 044904 (2006) uncertainty range  *    2  *  0.08   s  0.3 density correlation function density correlation function may differ from  r g

22. 22 Characterization III: medium response to energy loss

23. 23 R AA for  0 : medium density I C. Loizides hep-ph/0608133v2 I. Vitev W. Horowitz Use R AA to extract medium density: I. Vitev: 1000 < dN g /dy < 2000 W. Horowitz: 600 < dN g /dy < 1600 C. Loizides: 6 < < 24 GeV 2 /fm Statistical analysis to make optimal use of data Caveat: R AA folds geometry, energy loss and fragmentation

24. 24 What do we learn from R AA ? ~15 GeV  E=15 GeV Energy loss distributions very different for BDMPS and GLV formalisms But R AA similar! Renk, Eskola, hep-ph/0610059 Wicks et al, nucl-th/0512076v2 BDMPS formalism GLV formalism Need more differential probes

25. 25   nucl-ex/0504001 Energy dependence of R AA R AA at 4 GeV: smooth evolution with √s NN Agrees with energy loss models

26. 26 Medium response (I): Di-Hadron correlations on the near-side What is it ? ‘something’ coupling to long flow ? Can this quantify E-loss ? How to deal with it? Need to subtract for near-side studies? Components  Near-side jet peak  Near-side ridge  Away-side (and v 2 ) 3 < p t,trigger < 4 GeV p t,assoc. > 2 GeV Au+Au 0-10% preliminary Two distinct questions: Lesson: The near-side jet does interact with the medium associated  trigger

27. 27  “Ridge” + “Jet” yield vs Centrality preliminary Jet+Ridge (  ) Jet (  ) Jet  ) yield ,  ) N part “Jet” yield constant with N part “Ridge” yield increases with N part Effects nearly independent of particle species Jet Jet + Ridge

28. 28 STAR preliminary Central AuAu: Ridge, Jet Yield vs p T, trig p T, assoc p t,assoc. > 2 GeV Ridge yield ~ constant (slightly decreasing) vs. p T trig Ridge Jet “Jet spectrum” much harder than inclusive gets harder w/ increasing p t,trigger “Ridge spectrum” close to inclusive ~ independent of p t,trigger Central Ridge Persists up to highest p T trig STAR preliminary

29. 29 Medium Response (II) Away-Side shapes 0-12% 1.3 < p T assoc < 1.8 GeV/c 4.0 < p T trig < 6.0 GeV/c 6.0 < p T trig < 10.0 GeV/c Away-side: –Structures depend on range of p T. –becomes flatter with increasing p T trig –yield increases 3.0 < p T trig < 4.0 GeV/c AuAu 0-12% Central contribution to away-side becomes more significant with harder p T trig => fills dip Preliminary Away side

30. 30 Interpretations of away-side broadening Mach Cone/Shock wave T. Renk, J. Ruppert Stöcker, Casseldery-Solana et al Cherenkov radiation Gluon rad+Sudakov A. Polosa, C. Salgado V. Koch, A. Majumder, X-N. Wang Many explanations possible, need more input to conclude Or large k T from radial flow or energy loss Fries, Armesto et al, Hwa e.g.: Vitev, Phys. Lett. B630 (2005)

31. 31 3-particle correlations  13  12 0    13  12 0   Event by event deflection of jets Cone like structure in each event 3-particle  -  probes away-side structure: Distinguish event-by-event deflection vs conical (Mercedes) emission pattern However: Large backgrounds, background shapes not simple Tantalising results! Discussion/comparison of methods needed

32. 32 Characterization IV: Degrees of freedom

33. 33 Flavor dependence of yield scaling participant scaling for light quark hadrons (soft production) binary scaling for heavy flavor quark hadrons (hard production) strangeness is not well understood (canonical suppression in pp) PHENIX D-mesons up, down strange charm

34. 34 At higher pt: all particle v2 follows NCQ scaling STAR preliminary

35. 35 Light & strange baryon to meson ratios Can be explained with recombination (NCQ scaling)

36. 36 STAR preliminary Intriguing new result: all strange ratio  / 

37. 37 R. C. Hwa et al., nucl-th/0602024  -h correlation Near-side yield similar for , ,  triggered correlations Initial expectation:  dominantly from TTT recombination, no associated yield Revisited (at QM06): possible large contribution from reheated medium Experimental tests pending

38. 38 Summary We have first estimates of the viscosity of the Quark Gluon Liquid.  /s is close to the lower viscosity bound The medium response to heavy flavor is puzzling. Either the energy loss is too high or the required gluon density is not physical. The medium responds strongly to any high momentum probe (conical flow ?) We have more evidence for constituent quark scaling above T c. Do the degrees of freedom in the Quark Gluon Liquid have a dynamic mass ? Could there be a decoupling of the deconfinement transition and chiral symmetry restoration Is there another transition from the sQGP to the wQGP at LHC energies ?

39. 39 The future is bright A two prong approach: improved facility higher energy upgraded detectors & lower energy LHC in 2008: Large Hadron Collider with ALICE, CMS, ATLAS heavy ion programs RHIC-II in 2010: RHIC luminosity upgrade plus low energy running

40. 40 Weinberg’s 3 rd law of Theoretical Physics You may use any degrees of freedom you like to describe a physical system, but if you use the wrong ones, you’ll be sorry ! Lattice QCD based dynamic QCD vacuum visualization, Adelaide Group