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

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

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 First successful demo of stochastic cooling for bunched beams relied on state-of-art multi-GHz HV kicker and filtering out coherent bunch motion. 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

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

7 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. 26 TeV Fireball ! Lattice  c  Bj ~ 4.6 GeV/fm 3  Bj ~ 23.0 GeV/fm 3 Lattice Critical Density

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

9 Implications if Temperature ~ 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 T H ~ 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 Hydrodynamics with no viscosity matches data. *viscosity = resistance of liquid to shear forces (and hence to flow) Thermalization time  < 1 fm/c and  =20 GeV/fm 3 v2v2 p T (GeV) Perfect Fluid (AIP Story of the Year 2005)

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

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). Excellent example of nuclear theorists contributing to another field, and string theorists to ours. The Shear Viscosity of Strongly Coupled N=4 Supersymmetric Yang-Mills Plasma, G. Policasto, D.T. Son, A.O. Starinets, PRL 87: (2001). INT Program

14 Has string theory proven useful thus far? 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  Paradigm shift ‘strongly’ motivated by famous Gubser, Klebanov, Peet result

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

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

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

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

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

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

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

22 Quantitative Jet Quenching 00 h h Example: ASW Parton Energy Loss embedded in hydrodynamic bulk. Transport coeff. ~ 8 GeV 2 /fm Inconsistent for heavy quarks! ^ R AA I AA Charm,Beauty  e

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

24 Multi-Particle Jet Correlations Intriguing results of conical emission! If not a mach cone, what is the source?  Trig 22 11 Emission on opposite sides with the same trigger !

25 Return to the Phase Diagram There is considerable uncertainty in the location of the QCD critical point Counts Simulations (K + +K - )/(  + +  -) 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 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 ALICE at 18:15 Sunday June 15

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

30 50 nanoseconds T = 10 x T c 6 microseconds T c = 170 MeV 1.6 microseconds T = 2 x T c 400 nanoseconds T = 4 x T c Early Universe Universe spends bulk of QGP time as perfect fluid. 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.” 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. J. Nagle, now, “I believe we have reached Terra Firma.”

– First LHC Heavy Ion Physics November 4, – RHIC II with 10x luminosity and new precision era 2016 – FAIR 2000 – RHIC on-line 2005 – Perfect Fluid Perfect Fluid Universe GOLDENAGEGOLDENAGE