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The Quark Gluon Plasma and the Perfect Fluid

Quantifying Degrees of Perfection

Jamie NagleUniversity of Colorado, Boulder

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What do terms like “Quark Soup” and “Perfect Liquid” mean?

How does that compare with a “Quark Gluon Plasma”?

Good questions !

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Quark Gluon Plasma

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30Tg

Can we melt the hadrons and liberate quark and gluon degrees of freedom?

Energy density for “g” massless d.o.f.

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303 T

Hadronic Matter: quarks and gluons confinedFor T ~ 200 MeV, 3 pions with spin=0

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303222

8

782 Tcfasg

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3037 T

Quark Gluon Matter:8 gluons;

2 quark flavors, antiquarks,

2 spins, 3 colors37 !

Degrees of Freedom

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Lattice QCD Confirmation

Temperature / Tc

/T

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And it reaches 80% of the non-interacting gas limit.

QCD does reveal a transition (smooth cross over perhaps) with almost an order of magnitude change in the thermodynamic degrees of freedom.

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“Freely Roaming” Quarks and Gluons?“Quarks and gluons freely roam within the volume of the fireball created by the collision.”

This implies that thermodynamic degrees of freedom are associated with specific moving quasi-particles.

Quasi-particle = collective medium excitation that has a width which is much smaller than its energy and acts like a ballistic particle

Is this “freely roaming” picture right?

2000

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Crank the Energy Up and Do the Experiment !

10,000 virtual gluons, quarks, and antiquarks from the nuclear wavefunctions

are made physical in the laboratory !

What is the nature of this ensemble of partons?

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• Relativistic Heavy Ion Collider online since 2000.

• Design Au+Au energy and luminosity achieved.

• All experiments successfully taking data

• Polarized proton proton (spin) program underway

STAR

RHIC is doing great !

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Out of a maximum energy of 39.4 TeV in central Gold Gold reactions, 26 TeV is deposited in the fireball.

Energy density is far above the expected transition point.

26 TeV Fireball !

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0 fm/c

2 fm/c

7 fm/c

>7 fm/cDiagram from Peter Steinberg

Time Evolution

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, , 00, K, K, K, K*0*0(892), K(892), Kss00, , , p, d, , p, d, 00, , , , ,,

, , *(1385), *(1385), *(1520), ± , ,

(+ antiparticles)(+ antiparticles) in equilibrium at T > 170 MeV

What Happens to All That Energy?

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How Does the Matter Behave?

Simple answer is with a very high degree of collectivity.

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First time hydrodynamics without any viscosity describes heavy ion reactions.

*viscosity = resistance of liquid to shear forces (and hence to flow)

Thermalization time t=0.6 fm/c and =20 GeV/fm3

Like a Perfect Liquid?

v2

pT (GeV)

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Hydrodynamics• Assume early equilibration and initial geometry

• Equations of Motion

• Equation of State from lattice QCD

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Liquid HadronsPrevious hydrodynamics assumes

Liquid Hadrons

Mapping knows nothing of hadron structure, only masses.

This breaks down at higher pT!

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Flow “Knows” Quark Content !

FluidQuasiParticlesHadrons

Evidence for fluid breaking up into quasiparticles with quantum numbers of quarks before hadrons.

nq = number of valence quarks

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What Does This Mean?PHENIX: “Scaling suggests that partonic collectivity dominates the transverse expansion dynamics.”

STAR: “[Scaling indicates] a pre-hadronization state in which the flowing medium reflects quark degrees of freedom.”

Not exactly.

Inviscid fluids do not carry quasi-particles, almost by definition (they create viscosity).

Thus, thermodynamic degrees of freedom do not correspond to ballistic quasi-particles during the “perfect fluid time.”

However, as the fluid breaks down, it may be that quasi-particles are formed that have an anisotropy pattern. Then these quasi-particles hadronize and their anisotropy is imprinted on all hadrons.

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String Theory ?What could this have to do with our physics?

The Maldacena duality, know also as AdS/CFT correspondence, has opened a way to study the strong coupling limit using classical gravity where it is difficult even with lattice Quantum Chromodynamics.

It has been postulated that there is a universal lower viscosity bound for all strongly coupled systems, as determined in this dual gravitational system.

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Critical future goal to put the QCD data point on this plot.

?

Universal Viscosity Bound

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Probing the Matter

Calibrated LASER

Matter we want to study

CalibratedLight Meter

CalibratedHeat Source

Take an out of equilibrium probe and see how it equilibrates !

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Sometimes a high energy photon is created in the collision. We expect it to pass through the plasma without pause.

Probes of the Medium

Photons do not equilibrate with the matter.

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Sometimes we produce a high energy quark or gluon.

If the plasma is dense enough we expect the quark or gluon to be swallowed up.

Probes of the Medium

Quarks and Gluons do approach equilibration.

Can we determine a transport coefficient q?^

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(from quark and gluon jets)

Scaling of photons shows excellent calibrated probe.Quarks and gluons disappear into medium, except consistent with surface emission.

Sur

viva

l Pro

babi

lity

Size of Medium

Experimental Results

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10%)ty (Probabili

/fmGeV 24ˆ6 2

q

Constraint on Transport Coefficient

Future running and RHIC II luminosities will give a precision measure of the transport coefficient.

A major goal is to make such a constraint on other properties like /s as detailed before.

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Alternative: Put a pebble (or rock) in the stream….and watch something out of equilibrium then equilibrate.

Need 3-d relativistic viscous hydrodynamics to compare to bulk medium flow.

Significant theory milestone!

How to Quantify /s?

Charm Quark

Beauty QuarkPerfect Fluid?

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Charm Quark Probes

Teaney and Moore

Very large interactions suppress high pT and induce large flow.

Suppression Factor Flow

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Constraining /s Constraining /s • Rapp and van Hees

Phys.Rev.C71:034907,2005 – Simultaneously describe

RAA(E) and v2(e) with diffusion coefficient in range DHQ (2T) ~4-6

• Moore and Teaney Phys.Rev.C71:064904,2005 – Find DHQ/(/(+p)) ~ 6 for Nf=3

• Combining– +p = T s at B=0– This then gives

/s ~(1.33-2)/ 4

Within a factor of 2 of the bound. Need separation of c and b to pin this down better.

sDensityEntropy

4

)(4

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Jet correlations in proton-proton reactions.

Strong back-to-back peaks.

Jet correlations in central Gold-Gold.

Away side jet disappears for particles pT > 2 GeV

Jet correlations in central Gold-Gold.

Away side jet reappears for particles pT>200 MeV

Azimuthal Angular Correlations

Jet Quenching !

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Where Does the Energy Go?

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How does the near perfect liquid react to this large energy deposition? Color shock wave?

Reaction of the Medium

Sensitive to– Speed of sound– Equation of state

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ConclusionsRHIC program is operating very successfully.

The Quark-Gluon Plasma as “freely roaming” quasi-particles carrying the degrees of freedom unlikely at early stages.

Near Perfect Liquid Discovered.

Challenge is now to quantify and understand its properties.

Exciting future program at RHIC II and at the LHC.

Perfect Liquid?