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The Quark Gluon LiquidThe Quark Gluon LiquidThe AIP Science Story of 2005The AIP Science Story of 2005

R. Bellwied for the WSU RHIC group

WSU Physics Colloquium12-Dec-2005

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Did we serve up the perfect liquid ?Did we serve up the perfect liquid ?(Tampa press release, April 2005)(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 collisionsis 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.”

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The layout of my talkThe layout of my talkThe 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

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EllipticElliptic (anisotropic)(anisotropic) flow flow – – a strong indicator of early collectivitya strong indicator of early collectivity

Dashed lines: hard sphere radii of nuclei

Reactionplane

In-planeOu

t-o

f-p

lan

e

Y

XFlow

Flo

w

Y

XTime

Directed flow Elliptic flow

CentralcollisionMid-peripheralcollision

No elliptic flow,strong radial flowwith velocity

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Elliptic flow described by fluid dynamicsElliptic flow described by fluid dynamics

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Radial flow described by fluid dynamicsRadial flow described by fluid dynamics

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What does it mean ?What does it mean ?

Hydrodynamics describes the data:strong coupling

small mean free pathmany interactions

NOT ‘plasma-like’ !

The system exhibits strong collective flow:mass ordered elliptic & radial expansion with = 0.6 c

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A novel ideal liquid behaviorA novel ideal liquid behavior

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

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Constituent quarks might be relevantConstituent quarks might be relevant

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How strong is the coupling ?How strong is the coupling ?Navier-Stokes type calculationof viscosity – near perfect liquidViscous force ~ 0

Simple pQCD processes do not generate sufficient interaction strength (2 to 2 process = 3 mb)

v2

pT (GeV/c)

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An unexpected liquid phase with very An unexpected liquid phase with very

drastic thermodynamic properties ?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

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What could cause the strong coupling (d.o.f.) ?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

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Was it really unexpected ?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 thesystem becomepertubative ?

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Will the strong coupling disappear at higher Will the strong coupling disappear at higher energies ?energies ?

Different initial conditionsat RHIC and LHC ??Prediction: v2 should decrease

SPS

RHIC

LHCO.Kaczmarek et al. (hep-lat/0406036)

1.05 Tc

1.5 Tc

3 Tc

6 Tc12 Tc

coupling decreases as f (T,r)

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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’ connectionThe ‘cosmic’ connection

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400 times less viscous than water,10 times less viscous than superfluid helium !

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An example: lower viscosity bound in An example: lower viscosity bound in strong quantum field theorystrong 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)

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A little more detail..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/kB.

In n=9 t’Hoft coupled Quantum Field Theory: /s > h/4 kB

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 withinstrong 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 ?

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We need to actually measure the viscosity in heavy ion collisions.One tool: measure heavy flavor elliptic flow(Teaney, Petreczky (hep-p/0510021)

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 measurementOne intriguing future measurement

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An example: thermalization through An example: thermalization through Hawking mechanismHawking 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

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Many connections to QCDMany 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

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We have successfully createdthe Quark Gluon Plasma, anearly 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

ConclusionsConclusions

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The future is brightThe future is brightA three prong approach:

better facility expanded facility higher energy

                                                    

LHC (2008-2020 ?): Large Hadron Colliderwith ALICE, CMS, ATLAS heavy ion programs

RHIC-II (2008-2013):Upgrades toSTAR & PHENIX

EoS of sQGP QCD, CGC, QGP wQGP (?)

QCDLab (2013---):A high luminosityRHIC with eA andAA detectors

AGS

BOOSTER

RHIC

e-cooling

LINAC

EBIS

recirculating linac injector

5-10 GeV static electron ring