1 The Quark Gluon Liquid The AIP Science Story of 2005 R. Bellwied for the WSU RHIC group WSU Physics Colloquium 12-Dec-2005

2 Did we serve up the perfect liquid ? (Tampa press release, April 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 and RHIC collisions is unexpected and exhilarating. It may well have a profound impact on the physics of the twenty-first century.” said Dr. Raymond L. Orbach, Director of the DOE Office of Science. “Once again, the physics research sponsored by the Department of Energy is producing historic results,” said Secretary of Energy Samuel Bodman. “The DOE is the principal federal funder of basic research in the physical sciences, including nuclear and high-energy physics. With today’s announcement we see that investment paying off.”

3 The layout of my talk The evidence for the liquid phase The evidence for the partonic phase How liquid is it ? What do we still need to know ? The cosmic connection & the QCD connection

4 Elliptic (anisotropic) flow – a strong indicator of early collectivity Dashed lines: hard sphere radii of nuclei Reaction plane In-plane Out-of-plane Y X Flow Y X Time Directed flowElliptic flow Central collision Mid-peripheral collision No elliptic flow, strong radial flow with velocity 

5 Elliptic flow described by fluid dynamics

6 Radial flow described by fluid dynamics

7 What does it mean ? Hydrodynamics describes the data: strong coupling small mean free path many interactions NOT ‘plasma-like’ ! The system exhibits strong collective flow: mass ordered elliptic & radial expansion with  = 0.6 c

8 A novel ideal liquid behavior First time in Heavy-Ion Collisions a system created which, at low p t,is in quantitative agreement with ideal hydrodynamic model. The new phase behaves like an ideal liquid. But are the degrees of freedom partonic ?

9 Constituent quarks might be relevant

10 How strong is the coupling ? Navier-Stokes type calculation of viscosity – near perfect liquid Viscous force ~ 0 Simple pQCD processes do not generate sufficient interaction strength (2 to 2 process = 3 mb) v2 pT (GeV/c)

11 An unexpected liquid phase with very drastic thermodynamic properties ? The ideal liquid requires very strong interaction cross sections, vanishing mean free path and sudden thermalization (in less than 1 fm/c). Perturbative calculations of gluon scattering lead to long equilibration times (> 2.6 fm/c) and very small v2 The state above Tc can not be simple massless partons liquid ? liquid plasma gas

12 What could cause the strong coupling (d.o.f.) ? The simple parton-parton interaction between massless partons is not strong enough to generate fluid like behavior. Many alternatives have been suggested recently. All of them signal new physics just above the critical temperature Massive partons (quasi-particles) Very high gluon density (2 to 3 processes become important) Gluon saturation (CGC) Partonic bound states (glueballs) Heavy resonances above Tc

13 Was it really unexpected ? Present understanding of Quantum Chromodynamics (QCD): Lattice QCD predicted that at RHIC energies the Boltzmann limit of interactions (pQCD limit, ideal gas behavior) would not be reached. So when does the system become pertubative ?

14 Will the strong coupling disappear at higher energies ? Different initial conditions at RHIC and LHC ?? Prediction: v2 should decrease SPS RHIC LHC O.Kaczmarek et al. (hep-lat/ ) 1.05 T c 1.5 T c 3 T c 6 T c 12 T c coupling decreases as f (T,r)

15 a.) the equation of state of the QGP resembles features of black hole physics. b.) the degrees of freedom above Tc will be the building blocks of hadronic matter in the universe. Hadronization in matter might be different from hadronization in vacuum. c.) primordial fluctuations of conserved quantum numbers around the critical point might lead to measurable effects in the universe (matter-antimatter, charge, and strangeness distribution) The ‘cosmic’ connection

times less viscous than water,10 times less viscous than superfluid helium ! ? An example: lower viscosity bound in strong quantum field theory 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)

17 A little more detail.. A lower viscosity bound can be given by simple uncertainty principle arguments. The viscosity will depend on the mft (mean free time) between interactions. Therefore  /s > h/k B. In n=9 t’Hoft coupled Quantum Field Theory:  /s > h/4  k B This is not QCD because in QCD the coupling is weak (n -> 1). That could lead to transition effects. QCD is not a CFT, but within strong QFT’s the result night be universal and the theories are conformal. Example: N=4 SUSY Yang-Mills theory in Anti deSitter space is a good description of black hole physics RHIC parameters = quantum black hole features ?

18 We need to actually measure the viscosity in heavy ion collisions. One tool: measure heavy flavor elliptic flow (Teaney, Petreczky (hep-p/ ) Since quark mass is significantly higher than temperature of the system, the mfp of heavy mesons should be proportional to M/T. Quantitative description through diffusion coefficient D. The viscous drag coefficient  relates to the diffusion coefficient D through the Einstein relation: D = T/M   for heavy quarks can be estimated in lattice QCD One intriguing future measurement

19 An example: thermalization through Hawking mechanism Black holes emit thermalized Hawking radiation due to strongly varying accelerator gradients on both sides of the event horizon (splitting of e+e- pair from virtual photons). RHIC collisions might have black-hole like gradients due to very different gluon densities inside and outside the fireball (leads to  -gradients). This might explain sudden thermalization

20 Many connections to QCD Study fragmentation in and out of the medium Study extreme gluon saturation (Color Glass Condensate) ? Study QCD susceptibilities of conserved quantum numbers (strong parity violation, bound states above Tc) ? Lattice QCD –Map QCD masses and their evolution above the critical temperature –Map QCD susceptibilities (fluctuations) around critical point –Predict deconfinement and chiral symmetry properties in detail

21 We have successfully created the Quark Gluon Plasma, an early universe phase of matter, which might still exist in black holes. Now we need to understand its exciting properties: low viscosity rapid equilibration (thermalization) novel hadron formation mechanisms jet quenching and medium reaction temperature determination degrees of freedom Conclusions

22 The future is bright A three prong approach: better facility expanded facility higher energy LHC ( ?): Large Hadron Collider with ALICE, CMS, ATLAS heavy ion programs RHIC-II ( ): Upgrades to STAR & PHENIX EoS of sQGP QCD, CGC, QGP wQGP (?) QCDLab ( ): A high luminosity RHIC with eA and AA detectors AGS BOOSTER RHIC e- cooling LINAC EBIS recirculating linac injector 5-10 GeV static electron ring