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Properties of the sQGPProperties of the sQGPmeasured with STARmeasured with STAR

Rene BellwiedWayne State University

XLV International Winter Meeting on Nuclear Physics,

BORMIO 2007, Jan.13th-20th

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Did we serve up the perfect liquid ?Did we serve up the perfect liquid ?(The AIP Science Story of 2005)(The AIP Science Story of 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, cosmology and RHIC collisions is unexpected and exhilarating. It may well have a profound impact on the physics of the twenty-first century.”

Dr. Raymond L. Orbach Director of the DOE

Office of Science.

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microexplosions femtoexplosions

s 0.1 J 1 J

1017 J/m3 5 GeV/fm3 = 1036 J/m3

T 106 K 200 MeV = 1012 K

rate 1018 K/s 1035 K/s

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Major discoveries in AuAu collisionsMajor discoveries in AuAu collisions

‘The Big Three’‘The Big Three’(leading to the discovery of the sQGP (leading to the discovery of the sQGP

= the Perfect Quark Gluon Liquid)= the Perfect Quark Gluon Liquid)

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STAR, nucl-ex/0305015

energyloss

pQCD + Shadowing + Cronin

pQCD + Shadowing + Cronin + Energy Loss

# I: The medium is dense and partonic# I: The medium is dense and partonic

Deduced initial gluon density at = 0.2 fm/c dNglue/dy ≈ 800-1200

≈ 15 GeV/fm3, eloss = 15*cold nuclear matter

(compared to HERMES eA or RHIC dA) (e.g. X.N. Wang nucl-th/0307036)

?

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# II: The medium behaves like a liquid# II: The medium behaves like a liquid

x

yz

Strong collective flow:elliptic and radial expansion withmass ordering

requires partonic hydrodynamics:strong coupling,small mean free path,lots of interactionsNOT plasma-like more like a perfect liquid (near zero viscosity, d.o.f. ?)

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# III: The medium consists of constituent quarks ?# III: The medium consists of constituent quarks ?

baryonsbaryons

mesonsmesons

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Consequences of a perfect liquidConsequences of a perfect liquid All “realistic” hydrodynamic calculations for RHIC fluids to date

have assumed zero viscosity = 0 “perfect fluid”– But there is a (conjectured) quantum limit

– Where do “ordinary” fluids sit wrt this limit?

– RHIC “fluid” mightbe at ~2-3 on this scale (!)

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

sDensityEntropy

4

)(4

T=10T=101212 KK

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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Viscosity in Collisions Viscosity in Collisions Hirano & Gyulassy, Teaney, Moore, Yaffe, Gavin, etc.

supersymmetric Yang-Mills: s pQCD and hadron gas: s ~ 1

liquid ?

liquid

plasma

gas

d.o.f. in perfect liquid ? Bound states ?, constituent quarks ?, heavy resonances ?

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Suggested ReadingSuggested Reading November, 2005 issue of Scientific American

“The Illusion of Gravity” by J. Maldacena

A test of this prediction comes from the Relativistic Heavy Ion Collider (RHIC) at BrookhavenNational Laboratory, which has been colliding gold nuclei at very high energies. A preliminary analysis of these experiments indicates the collisions are creating a fluid with very low viscosity. Even though Son and his co-workers studied a simplified version of chromodynamics, they seem to have come up with a property that is shared by the real world. Does this mean that RHIC is creating small five-dimensional black holes? It is really too early to tell, both experimentally and theoretically. (Even if so, there is nothing to fear from these tiny black holes-they evaporate almost as fast as they are formed, and they "live" in five dimensions, not in our own four-dimensional world.)

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A few introductory remarksA few introductory remarks At RHIC we found strongly coupled partonic, collective

matter (sQGP). The discovery phase has been concluded. The

characterization phase is just beginning. What do we need to know ?

LET’S BE QUANTITATIVE:– Let’s determine the viscosity bound at RHIC– Let’s determine the energy loss characteristics in the dense medium– Let’s determine the medium response to the energy loss– Let’s determine the degrees of freedom in the liquid phase

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Characterization I:Characterization I: flow, viscosity flow, viscosity

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A new picture of an old idea, energy dependence of A new picture of an old idea, energy dependence of applicability of ideal hydrodynamicsapplicability of ideal hydrodynamics

Consistent v2/ scaling for all energies and collision systems.

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χ2 minimum resultD->e

2σ

4σ

1σ

Even charm flowsEven charm flows strong elliptic flow of electrons from

D meson decays → v2D > 0

v2c of charm quarks?

recombination Ansatz: (Lin & Molnar, PRC 68 (2003) 044901)

universal v2(pT) for all quarks simultaneous fit to , K, e v2(pT)

eT

D

cqT

D

uqT

D vpm

mbvp

m

mavpv 2222 )()()(

a = 1

b = 0.96

2/ndf: 22/27

within recombination model: charm flows like light quarks!

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How can a heavy quark flow like the How can a heavy quark flow like the light quarks ? light quarks ?

Many interactions of the heavy quark in the partonic phase (thermalization ?)

Ideal hydro - low viscosity, high Diffusion

What are the degrees of freedom ? : dressed up constituent quarks, bare heavy quarks, gluons, colorless bound states (glueballs ?), quasi-D’s (isotropic elastic parton scattering (Rapp / van Hees, this workshop)).

Let’s measure v2 for D (through hadron channels), B-mesons (through J/channelsand onium states.

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Characterization II:Characterization II: heavy flavor energy loss heavy flavor energy loss

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An important detail: the medium is not totally opaqueAn important detail: the medium is not totally opaqueThere are specific differences to the flavor of the probeThere are specific differences to the flavor of the probe

Theory: there are two types of e-loss:radiative and collisional, plus dead-cone effect for heavy quarksFlavor dependencies map out the process of in-medium modification

Experiment: there arebaryon/meson differences

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BUT: heavy quarks show same e-loss than light quarksBUT: heavy quarks show same e-loss than light quarks

RAA of electrons from heavy flavor decay

Describing the suppression is difficult for models

radiative energy loss with typical gluon densities is not enough

(Djordjevic et al., PLB 632(2006)81) models involving a very opaque medium agree

better (qhat very high !!)

(Armesto et al., PLB 637(2006)362) collisional energy loss / resonant elastic

scattering

(Wicks et al., nucl-th/0512076, van Hees & Rapp, PRC 73(2006)034913)

heavy quark fragmentation and dissociation in the medium → strong suppression for charm and bottom (Adil & Vitev, hep-ph/0611109)

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Constraining medium viscosity Constraining medium viscosity /s/s Simultaneous description of

STAR R(AA) and PHENIX v2for charm. (Rapp & Van Hees, PRC 71, 2005)

Ads/CFT == /s ~ 1/4 ~ 0.08 Perturbative calculation of D (2t) ~6

(Teaney & Moore, PRC 71, 2005) == /s~1

transport models require– small heavy quark

relaxation time– small diffusion coefficient

DHQ x (2T) ~ 4-6– this value constrains the

ratio viscosity/entropy /s ~ (1.3 – 2) / 4 within a factor 2 of conjectured lower quantum bound consistent with light hadron

v2 analysis electron RAA ~ 0 RAA at high pT - is bottom suppressed as well?

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An alternate idea (Abdel-Aziz & Gavin)An alternate idea (Abdel-Aziz & Gavin)

viscous liquid pQGP ~ HRG ~ 1 fm

nearly perfect sQGP ~ (4 Tc)-1 ~ 0.1 fm

Abdel-Aziz & S.G

Ts

Level of viscosity will affect the diffusion of momentum correlationskinematic viscosity

effect on momentum diffusion:

limiting cases:

wanted:wanted: rapidity dependence of momentum correlation rapidity dependence of momentum correlation functionfunction

T 1( /s)

Broadening from viscosity

d

d 2

4 ( )

2 ,

QGP + mixed phase + hadrons T()

= width of momentum covariance C in rapidity

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we want: 2

2

1t

jitjti ppp

NC

STAR measurementSTAR measurement

STAR measures:

maybe n 2* STAR, PRC 66, 044904 (2006)

uncertainty range

* 2* 0.08 s 0.3

N p t :n pti pt ptj pt ij

N 2C pt

2(density correlations)

density correlation functiondensity correlation function may differ from rg

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Characterization III:Characterization III: medium response to energy loss medium response to energy loss

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RRAAAA for for 00: medium density I: medium density I

C. Loizideshep-ph/0608133v2

I. Vitev

W. HorowitzUse RAA to extract medium density:

I. Vitev: 1000 < dNg/dy < 2000

W. Horowitz: 600 < dNg/dy < 1600

C. Loizides: 6 < < 24 GeV2/fmq̂

Statistical analysis to make optimal use of dataCaveat: RAA folds geometry, energy loss and fragmentation

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What do we learn from RWhat do we learn from RAAAA??

~15 GeV

E=15 GeV

Energy loss distributions very different for BDMPS and GLV formalisms

But RAA similar!

Renk, Eskola, hep-ph/0610059

Wicks et al, nucl-th/0512076v2

BDMPS formalismGLV formalism

Need more differential probes

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nucl-ex/0504001

Energy dependence of REnergy dependence of RAAAA

RAA at 4 GeV: smooth evolution with √sNN

Agrees with energy loss models

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Medium response (I): Di-Hadron Medium response (I): Di-Hadron correlations on the near-sidecorrelations on the near-side

What is it ? ‘something’ coupling to long flow ? Can this quantify E-loss ?

How to deal with it?Need to subtract for near-side studies?

Components

Near-side jet peak

Near-side ridge

Away-side (and v2)

3 < pt,trigger < 4 GeV

pt,assoc. > 2 GeVAu+Au 0-10%

preliminary

Two distinct questions:

Lesson: The near-side jet does interact with the medium

associated

trigger

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“ “Ridge” + “Jet” yield vs CentralityRidge” + “Jet” yield vs Centrality

preliminaryJet+Ridge ()Jet ()Jet)

yie

ld,

)

Npart

“Jet” yield constant

with Npart

“Ridge” yield increases

with Npart

Effects nearly independent of particle species

JetJet + Ridge

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STAR preliminary

Central AuAu: Ridge, Jet Yield vs pCentral AuAu: Ridge, Jet Yield vs pTT,, trig trig p pTT,,assocassoc

pt,assoc. > 2 GeV

Ridge yield ~ constant

(slightly decreasing) vs. pT

trig

RidgeJet

“Jet spectrum” much harder than

inclusive

gets harder w/ increasing

pt,trigger

“Ridge spectrum” close to

inclusive

~ independent of pt,trigger

Central

Ridge Persists up to highest pT trig

STAR preliminary

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Medium Response (II) Away-Side shapesMedium Response (II) Away-Side shapes

0-12%

1.3 < pTassoc < 1.8

GeV/c

4.0 < pTtrig < 6.0 GeV/c 6.0 < pT

trig < 10.0 GeV/c

Away-side:

– Structures depend on range of pT.

– becomes flatter with increasing pT

trig

– yield increases

3.0 < pTtrig < 4.0 GeV/c

AuAu 0-12%

Central contribution to away-side

becomes more significant with

harder pTtrig => fills dip

PreliminaryAway side

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Interpretations of away-side broadeningInterpretations of away-side broadeningMach Cone/Shock wave

T. Renk, J. Ruppert

Stöcker, Casseldery-Solana et al

Cherenkov radiation

Gluon rad+Sudakov

A. Polosa, C. Salgado

V. Koch, A. Majumder, X-N. Wang Many explanations possible,

need more input to conclude

Or large kT from radial flow or energy loss Fries, Armesto et al, Hwa

e.g.: Vitev, Phys. Lett. B630 (2005)

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3-particle correlations3-particle correlations

1

3

12

0

13

12

0

Event by event deflection of jets

Cone like structure in each event

3-particle - probes away-side structure:Distinguish event-by-event deflection vs conical (Mercedes) emission pattern

However: Large backgrounds, background shapes not simple

Tantalising results! Discussion/comparison of methods needed

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Characterization IV:Characterization IV:Degrees of freedomDegrees of freedom

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Flavor dependence of yield scalingFlavor dependence of yield scaling

• participant scaling for light quark hadrons (soft production)• binary scaling for heavy flavor quark hadrons (hard production)• strangeness is not well understood (canonical suppression in pp)

PHENIX D-mesons

up, down strange charm

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At higher pt: all particle v2 follows NCQ scalingAt higher pt: all particle v2 follows NCQ scaling

STAR preliminarySTAR preliminary

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Light & strange baryon to meson ratiosLight & strange baryon to meson ratios

Can be explained with recombination (NCQ scaling)

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STAR preliminary

Intriguing new result: all strange ratio Intriguing new result: all strange ratio //

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R. C. Hwa et al., nucl-th/0602024

-h correlation-h correlation

Near-side yield similar for , , triggered correlations

Initial expectation: dominantly from TTT recombination, no associated yield

Revisited (at QM06): possible large contribution from reheated mediumExperimental tests pending

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SummarySummary We have first estimates of the viscosity of the Quark

Gluon Liquid. /s is close to the lower viscosity bound The medium response to heavy flavor is puzzling.

Either the energy loss is too high or the required gluon density is not physical. The medium responds strongly to any high momentum probe (conical flow ?)

We have more evidence for constituent quark scaling above Tc. Do the degrees of freedom in the Quark Gluon Liquid have a dynamic mass ?

Could there be a decoupling of the deconfinement transition and chiral symmetry restoration

Is there another transition from the sQGP to the wQGP at LHC energies ?

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The future is brightThe future is brightA two prong approach:

improved facility higher energyupgraded detectors & lower energy

                                                    

LHC in 2008: Large Hadron Colliderwith ALICE, CMS, ATLAS heavy ion programs

RHIC-II in 2010:RHIC luminosity upgrade plus lowenergy running

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Weinberg’s 3Weinberg’s 3rdrd law of law ofTheoretical PhysicsTheoretical Physics

You may use any degrees of

freedom you like to describe a

physical system, but if you use the

wrong ones, you’ll be sorry !

Lattice QCD based dynamic QCD vacuum visualization, Adelaide Group