The Golden Age for Studying Hot QCD Matter

1. The Golden Age for Studying Hot QCD Matter 2008 Annual Meeting of the Division of Nuclear Physics October 23, 2008; Oakland, CA. Jamie Nagle University of Colorado

2. Quark Gluon Plasma without color confinement Goal is to explore and quantitatively describe this phase diagram Lattice QCD Big change in degrees of freedom Reaches 80% of the non-interacting gas limit Weakly interacting quarks & gluons (?)

3. Heavy Ion Collisions 10,000 virtual gluons, quarks, and antiquarks from the nuclear wavefunctions are made physical in the laboratory !

4. Relativistic Heavy Ion Collider on-line in 2000.

5. fiber optic links wave links RHIC Successes • Experiments BRAHMS, PHENIX, PHOBOS, STAR • RHIC White Papers amongst most cited in all of nuclear physics • Major detector upgrades to PHENIX and STAR • - enabling precision measurements and new critical observables • Order of magnitude heavy ion luminosity increase (RHIC II) for rare probes • Original plan – electron cooling ~$100M • New plan – stochastic cooling for ~$10M and earlier availability ~2012 • Major accelerator division breakthrough First successful demo of stochastic cooling for bunched beams relied on state-of-art multi-GHz HV kicker and filtering out coherent bunch motion.

6. 0 fm/c 2 fm/c 7 fm/c >7 fm/c Diagram from Peter Steinberg Time Evolution

7. Lattice ec 26 TeV Fireball ! eBj ~ 23.0 GeV/fm3 eBj ~ 4.6 GeV/fm3 Lattice Critical Density Out of a maximum energy of 39.4 TeV in central Gold Gold reactions, 26 TeV is available in the fireball. Energy density is far above the expected transition point.

8. TAA scaled pp + Exponential Fit to pp NLO pQCD (W. Vogelsang) Thermalized hot matter emits EM radiation Emission rate and distribution consistent with equilibrated matter: t < 1 fm/c and T > 2 x Tc ! QGP Shine !?! Gold-Gold Direct Photons Ti = 300-600 MeV Proton-Proton Direct Photons PHENIX: arXiv:0804.4168

9. Implications if Temperature ~ 300-600 MeV? Hagedorn (1968) calculated a limiting temperature due to exponential increase in hadron levels. Adding more energy only excites more states, no more increase in temperature. Cannot exceed TH ~ 170 MeV, except through change in Degrees of Freedom (e.g. QGP). W.A. Zajc

10. How Does the Matter Behave? Simple answer is with a very high degree of collectivity.

11. Perfect Fluid (AIP Story of the Year 2005) Hydrodynamics with no viscosity matches data. v2 pT (GeV) Thermalization time t < 1 fm/c and e=20 GeV/fm3 *viscosity = resistance of liquid to shear forces (and hence to flow)

12. Viscosity Review Honey – viscosity decreases at higher temperatures viscosity increases with stronger coupling Weak coupling (s~0) Inhibited diffusion ↓ Small viscosity ↓ Perfect fluid ↓ Strong Coupled QGP (i.e. sQGP) <px> top region <px> bottom region Strong coupling (s↑)

13. Calculating viscosity is very difficult in a strongly-coupled gauge theory (e.g. QCD). A (supersymmetric) pseudo-QCD theory can be mapped to a 10-dimensional classical gravity theory on the background of black 3-branes (String Theory). The Shear Viscosity of Strongly Coupled N=4 Supersymmetric Yang-Mills Plasma, G. Policasto, D.T. Son, A.O. Starinets, PRL 87: 081601 (2001). INT Program Excellent example of nuclear theorists contributing to another field, and string theorists to ours.

14. Has string theory proven useful thus far? Paradigm shift ‘strongly’ motivated by famous Gubser, Klebanov, Peet result Do we learn anything about string theory? These are real predictions from quantum gravity. If confirmed in the gauge dual quantitatively, does that prove strings are a correct theory of quantum gravity? Some theorists say yes  Some no 

15. What is h/s for QCD matter at a trillion Kelvin? Lowest Bound! ? QCD Gas-Liquid Phase Transition Superfluidity Transition

16. Connections / Impact T. Schafer, arXiv:0707.1540v1 (2007). Strongly interacting Li atoms h/s ~ 7 x 1/4p

17. How to Quantify h/s? Need 3-d relativistic viscous hydrodynamics to compare to bulk medium flow. Theory milestone. h/s ~ 0 h/s = 1/4p h/s = 2 x 1/4p h/s = 3 x 1/4p * with caveats

18. c , b e Suppression RHIC II AuAu 20 nb-1 ce Flow c,be be Examples: PHENIX Silicon VTX and fVTX, STAR Heavy Flavor Tracker Charm and Beauty Heavy quarks are pushed around by medium. Theory comparisons imply h/s = (1.3-2.0) x 1/4p Displaced vertex measurements and luminosity will allow separation of charm and beauty, which is critical for fully constraining h/s. DHF = 30/2pT DHF = 6/2pT DHF = 4/2pT Suppression Flow Phys. Rev. C71, 034907, 2005. Phys. Rev. C71, 064904, 2005. Transverse Momentum

19. Perfect Fluid Independent of Composition Quark Recombination Perfect Fluid composed of Quark-like Quasiparticles?? Time

20. Reconciling these Pictures? * Perfect fluids cannot have well defined quasiparticles! Causes dissipation. 2nd Paradigm shift: Change in thermodynamic Degrees of Freedom, but no Quasiparticles carrying the D.o.F. in the Quark-Gluon Plasma. Weakly coupled limit from kinetic theory: > 1 / 4p Identify mean free path l = v t and t = 2 / G ~ Order(1) Think lmfp ~ lDeBroglie Perhaps a chance for quasiparticles at fluid breakup stage, but this remains a puzzle. L.A. Linden Levy, JN, C. Rosen, P. Steinberg.e-Print: arXiv:0709.3105 [nucl-th]

21. Probes of the Medium If the plasma is dense enough we expect a high pT quark or gluon to be swallowed up. Quarks and Gluons do approach equilibration. Can we determine a transport coefficient q? Why are heavy quarks just as suppressed? ^

22. Quantitative Jet Quenching Charm,Beautye p0 RAA h Example: ASW Parton Energy Loss embedded in hydrodynamic bulk. Transport coeff. <q> ~ 8 GeV2/fm Inconsistent for heavy quarks! IAA h ^

23. Run 4 0.2 nb-1 Central AuAu Peripheral AuAu Reaction of the Medium What is the near perfect liquid reaction to this energy? Sensitive to • Speed of sound • Equation of state Three particle correlations needed requiring significant luminosity.

24. Multi-Particle Jet Correlations fTrig f1 f2 Emission on opposite sides with the same trigger ! Intriguing results of conical emission! If not a mach cone, what is the source?

25. Simulations Counts (K++K-)/(++-) Return to the Phase Diagram There is considerable uncertainty in the location of the QCD critical point Detector upgrades needed and improved luminosity at lowest energies for rare signals. Study of a phase transition in a fundamental theory without accidental scales.

26. RHIC low energy program already underway. FAIR (Facility for Antiproton and Ion Research) at GSI Just 3000 events! Heavy ion program start 2016 High intensity beams, fixed target configuration.

27. LHC Heavy Ion Energy Frontier ATLAS CMS ALICE Enormous excitement building, first heavy ions in 2010. New discoveries? How does the system evolve at higher energy? Energy Loss/Jets Entropy Production Flow

28. First particles created by the LHC as seen in ALICEat 18:15 Sunday June 15

29. 400 nanoseconds T = 4 x Tc 1.6 microseconds T = 2 x Tc 6 microseconds Tc = 170 MeV LHC Perfect Fluid? Ideal Gas RHIC Perfect Fluid Z. Fodor – Lattice 2007 50 nanoseconds T = 10 x Tc Early Universe

30. 400 nanoseconds T = 4 x Tc 1.6 microseconds T = 2 x Tc 6 microseconds Tc = 170 MeV Universe spends bulk of QGP time as perfect fluid. Are there implications? Smaller diffusion during QGP era, but not clear if any consequences. Worthy of further scrutiny. If nothing survived, then only way to verify this early state is with experimentation on earth. • M. Turner, in September 2003 Physics Today: • “...for more than 20 years in public lectures I have been explaining how the universe began from quark soup; until the Relativistic Heavy Ion Collider at Brookhaven produces evidence for quark-gluon plasma, I am not on totally firm ground.” 50 nanoseconds T = 10 x Tc Early Universe • J. Nagle, now, • “I believe we have reached Terra Firma.”

31. Nuclear Physicists Rock the Vote! 2000 – RHIC on-line 2005 – Perfect Fluid G O L D E N A G E November 4, 2008 Perfect Fluid Universe 2010 – First LHC Heavy Ion Physics 2012 – RHIC II with 10x luminosity and new precision era 2016 – FAIR