Evidence for a Q u a r k - G l u o n Plasma in Relativistic Heavy Ion Collisions

John Harris (Yale) QCD – String Theory Meets Collider Physics, DESY 9/28/07

Heavy Ions – Results and InterpretationEvidence for a Quark-Gluon Plasma in Relativistic

Heavy Ion Collisions


Modifications to s

heavy quark-antiquark coupling at finite T from lattice QCD O.Kaczmarek, hep-lat/0503017

Constituents - Hadrons, dressed quarks, quasi-hadrons, resonances?

Coupling strength variesinvestigates (de-)confinement, hadronization, & intermediate objects.

low Q2high Q2

D. Gross

H.D. Politzer

F. Wilczek

QCD Asymptotic Freedom (1973)

Nobel Prize 2005

“Before [QCD] we could not go back further than 200,000 years after the Big Bang. Today…since QCD simplifies at high energy, we can extrapolate to very early times when nucleons melted…to form a quark-gluon plasma.” David Gross, Nobel Lecture (RMP 05)


Phase Diagram of QCD MatterT

emp

erat

ure

baryon density

Early universe

nucleinucleon gas

hadron gascolor

superconductor

quark-gluon plasma

Tc

~ 1

70

Me

V

0

Critical point ?

vacuum

CFLNeutron stars

see: Alford, Rajagopal, Reddy, Wilczek Phys. Rev. D64 (2001) 074017L

HC

RHIC


Quark-Gluon Plasma

• Establish properties of QCD at high T (and density?)

• Can we make the primordial quark-gluon soup in the lab?

Quark-Gluon Plasma (Soup)

Standard Model Lattice Gauge Calculations

predict QCD Deconfinement phase transition

at Tc ~ 175 MeV (c ~ 0.5 GeV / fm3) Cosmology Quark-hadron phase transition in

early Universe

gravity electro-electro-magnetismagnetis

mm

weakstrong


Relativistic Heavy Ion Collider

RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

3.8 km circle

v = 0.99995

speed of light


Relativistic Heavy Ion Collider and Experiments

STARSTAR


Space-time Evolution of RHIC Collisions

e

space

time jet

Hard Scattering + Thermalization (< 1 fm/c)

AuAu

Exp

ansi

on

Hadronization

p K

Freeze-out(~ 10 fm/c)

QGP (~ few fm/c)

e


Ultra-Relativistic Heavy Ion Collisions

General Orientation

Hadron (baryons, mesons) masses ~ 1 GeV

Hadron sizes ~ 10-15 meters (1 fm ≡ 1 fermi)

RHIC Collisions

Ecm = 200 GeV/nn-pair

Total Ecm = 40 TeV

Gold nucleusdiameter = 14 fm

= 100 (Lorenz contracted)

= (14 fm/c) / ~ 0.1 fm/c

Interaction of Au nuclei complete in few tenths fm/c


Ultra-Relativistic Heavy Ion Collision at RHIC


PHOBOS

Au + Au

On the “First Day” (at RHIC)

Large energy densities dn/ddET/d

GeV/fm3 critical

x nuclear density

Large collective flow

ed. - “completely unexpected!”

Due to large early pressure gradients, energy & gluon densities

Requires hydrodynamics and quark-gluon equation of state

Quark flow & coalescence constituent quark degrees of freedom!

1

PHENIX

Initial Observations:Large produced particle multiplicities

ed. - “less than expected! gluon-saturation?”

dnch/d |=0 = 670, Ntotal ~ 7500

15,000 q +q in final state, > 92% are produced quarks

CGC?


How do RHIC Collisions Evolve?

b

1) Superposition of independent p+p:

momenta randomrelative to reaction plane

Reaction plane


How do RHIC Collisions Evolve?

b


2) Evolution as a bulk system


High densitypressureat center

“zero” pressurein surrounding vacuum

Pressure gradients (larger in-plane) push bulk “out” “flow”

more, faster particles seen in-plane



2) Evolution as a bulk system

Pressure gradients (larger in-plane) push bulk “out” “flow”

more, faster particles seen in-plane

N

-RP (rad)0 /2 /4 3/4

N

-RP (rad)0 /2 /4 3/4


Azimuthal Angular Distributions


On the First Day at RHIC - Azimuthal DistributionsSTAR, PRL90 032301 (2003)

b ≈ 4 fm

“central” collisions

b ≈ 6.5 fm

midcentral collisions

Top view

Beams-eye view

1


STAR, PRL90 032301 (2003)

b ≈ 4 fmb ≈ 6.5 fmb ≈ 10 fm

peripheral collisions

Top view

Beams-eye view

On the First Day at RHIC - Azimuthal Distributions1


Elliptic Flow Saturates Hydrodynamic Limit

• Azimuthal asymmetry of charged particles: dn/d ~ 1 + 2 v2(pT) cos (2) + ...

x

z

y

curves = hydrodynamic flowzero viscosity, Tc = 165 MeV

1

Mass dependence of v2

Requires -

• Early thermalization (0.6 fm/c)

• Ideal hydrodynamics

(zero viscosity)

“nearly perfect fluid”

• ~ 25 GeV/fm3 ( >> critical )

• Quark-Gluon Equ. of State


Identified Hadron Elliptic Flow ComplicatedComplicated v2(pT) flow pattern is observed for identified hadrons

d2n/dpTd ~ 1 + 2 v2(pT) cos (2 )

Baryons

Mesons

If the flow established at quark level, it is predicted to be simple KET KET / nq , v2 v2 / nq , nq = (2, 3 quarks) for (meson, baryon)

15000 quarksflow collectively


Vary System Size to Investigate Viscous Effects

v2 scales with system size and eccentricity PHENIX, nucl-ex/0608033

Eccentricity: = <x2 – y2> / <x2 + y2>

For perfect hydrodynamics (no viscosity):

v2 (pT) / independent of centrality

b

b

v2 (pT) /


Collision Centrality Dependence of the Flow

large ← impact parameter → small

• QGP + hadron fluidsOvershoot at large impactparameter

• QGP fluid and hadron gasReasonable reproductionCaveat: fluctuation effects

• Hadron gasUndershoot at any impactparameters

Fluid: Ideal hydrodynamicsGas: Boltzmann equation

Impossible to interpret data from hadronic degree of freedom only.

T.Hirano, Y.Nara, et al.(’06); M. Isse; M. Gyulassy


If baryons and mesons form

from independently flowing quarks

then

quarks are deconfined

for a brief moment (~ 10 -23 s), then hadronization!

Transport in gases of strongly-coupled atoms

RHIC fluid behaves like this –

a strongly coupled fluid.

Universality of Classical Strongly-Coupled Systems?

Universality of classical strongly-coupled systems? Atoms, sQGP, ……. AdS/CFT…… K.M. O’Hara et al

Science 298 (2002) 2179


Use strongly coupled N = 4 SUSY YM theory.

Derive a quantum lower viscosity bound: s > 1/4

AdS5/CFT – a 5D Correspondence of 4D Strongly-Coupled Systems

• Analogy between black hole physics and equilibrium thermodynamics

• Solutions possess hydrodynamic characteristicsSimilar to fluids – viscosity, diffusion constants,….

our world - 3 + 1 dim brane

horizon

Extra dim

ension

(the bulk)

MULTIPLICITY

Entropy Black Hole Area

DISSIPATION

Viscosity Graviton Absorption


Ultra-low (Shear)Viscosity Fluids

4 s

Quantum lower viscosity bound: s > 1/4 (Kovtun, Son, Starinets)

From strongly coupled N = 4 SUSY YM theory.

2-d Rel Hydro describes STAR v2 data with /s 0.1 near lower bound!

s (limit) = 1/4

s (water) >10QGP

T = 2 x 1012 K


What about the Viscosity?

√s = 200 GeV Au + Au

Comparing theory and experiment to extract viscosity - D. Teaney

estimate viscous corrections to spectra and elliptic flow using hydrodynamics

s = 4/3sT (sound attenuation length)

AdS/CFT: s/ = 1/(3T) ~ 0.11

Need viscous hydrodynamics a couple of years away……


“The RHIC fluid may be the

least viscous fluid ever seen”

The American Institute of Physics

announced the RHIC quark-gluon liquid

as the top physics story of 2005!see http://www.aip.org/pnu/2005/

John Harris (Yale) ISSP’06 Erice, Sicily, Italy, 29 Aug – 7 Sep 2006

It Flows - Is It Really Thermalized?

“Chemical” equilibration (particle yields & ratios):

Particles yields represent equilibrium abundances

universal hadronization temperature

Small net baryon density K+/K-,B/B ratios) B ~ 25 - 40 MeV

Chemical Freezeout Conditions T = 177 MeV, B = 29 MeV T ~ Tcritical (QCD)


QCD Phase Diagram

At RHIC:

T = 177 MeV

T ~ Tcritical (QCD)


Particles are thermally distributed and flow collectively,

at universal hadronization temperature T = 177 MeV!


On the “Second” Day (~ Year) at RHIC

Probing Hot QCD Matter with Hard-Scattered Probes

hadrons

leading particle

hadrons

leading particle

parton energy loss: modification of jets and leading particles & jet-correlations


High Momentum Hadrons Suppressed - Photons Not

Photons

Hadrons factor 4 – 5 suppression

dev/

AAAA /

coll pp

NR

N N

Deviations from binary scaling of hard collisions:


Energy Loss of Hard Scattered Parton

devEnergy loss requires large

pT = 4.5 – 10 GeV/c

2ˆ 5 10 GeV /fmq (Dainese, Loizides, Paic, hep-ph/0406201)

Much larger energy loss than expected from pQCD

Pion gas

QGP

Cold nuclear matter

RHIC data

sQGP

R. Baier


AdS5/CFT Again! - Initial Results on Jet Quenching

H. Liu, K. Rajagopal and U. A. Wiedemann, arXiv:hep-ph/0605178, recent PRL

from J. J. Friess, S. S. Gubser and

G. Michalogiorgakis,arXiv:hep-th/0605292.


pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

RAA of Heavy Quarks from Non-photonic Electrons

Suppression observed

~ 0.4-0.6 in 40-80% centrality

~ 0.3 -0.4 in 10-40%

~ 0.2 in 0-5%

Max suppression at pT ~ 5-6 GeV

Theories currently cannot describe the data! Only c contribution describes RAA but not p + p spectra

Heavy quarks suppressed like light quarks

STAR, nucl-ex/060712


Heavy Quark Suppression and Elliptic Flow

• large suppression &

large v2 of electrons

→ charm thermalization

• transport models require

– small heavy quark relaxation time

– small diffusion coefficient DHQ x (2T) ~ 4-6

– constrains viscosity/entropy

• /s ~ (1.5 – 3) / 4• within factor 2 - 3 of

conjectured lower

quantum bound

• consistent with light hadron v2 analysis

PHENIX, nucl-ex/0611018


Hard Scattering (Jets) as a Probe of Dense Matter II

Jet event in eecollision STAR p + p jet event

Can we see jets in high energy Au+Au?

STAR Au+Au (jet?) event


Where Does the Energy Go? dev

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 in particles pT > 200 MeV

Azimuthal Angular CorrelationsLost energy of away-side jet is redistributed to rather large angles!

Color wakes?

J. Ruppert & B. Müller

Mach cone from sonic boom?

H. Stoecker

J. Casalderrey-Solana & E. Shuryak

Cherenkov-like gluon radiation?

I. Dremin

A. Majumder, X.-N. Wang


Response of the Medium

Measure low-pT associated hadrons

• Shapes of jets are modified by the medium– Mach cone?– Cerenkov?– Color wakes? ….. Other….

2.5 < pTtrig < 4.0 GeV/c

1.0 < p

Ta

ssoc <

2.5 G

eV/cSTAR Preliminary

2.5 < pTtrig < 4.0 GeV/c

PHENIX preliminary

2.0 < p

Ta

ssoc <

3 GeV

/c

• Properties of the medium can be determined from these shapes!

– Sound velocity– Di-electric constant


Response of the Medium in AdS/CFT

hep-ph/0706.0368

v = vs v >> vs

Also see: Gubser, Pufu, Yarom, hep-th/0706.0213


The suppression of high pT hadrons and the quenching of jets

indicates the presence of a high density, strongly-coupled

colored medium. !


Pedestal&flow subtracted

Hard Scattering Conclusions

High Pt hadrons suppressed in central Au + Au Back-to-back Jets Di-jets in p + p, d + Au

(all centralities) Away-side jets quenched

in central Au + Auemission from surfacestrongly interacting medium

x


Conclusions about a QGP at RHIC

• Large > c (T > Tc) system – QCD vacuum “melts” – NOT hadrons

• Thermalized system of quarks and gluons – NOT just q & g scattering

Large elliptic & radial flow fluid flow (“perfect”!)

Heavy quark (charm) flow (not shown)

Particle ratios fit by thermal model T = 177 MeV ~ Tc (lattice QCD)

• System governed by quark & gluon Equation of State – NOT hadronic

Flow depends upon particle (constituent quark & gluon) masses

QGP EoS,, quark coalescence

• Deconfined system of quarks and gluons – NOT hadrons

Flow already at quark level, charmonium suppression (tbd)

• NOT a Weakly-interacting QGP (predicted by Lattice QCD)

Strongly interacting quarks and gluons ….degrees of freedom (tbd)

• Strongly-interacting QGP (NOT predicted by Lattice QCD)

Suppression of high pT hadrons, away-side jet quenched

Large opacity (energy loss) extreme gluon/energy densities

strongly-interacting QGP (sQGP)


Future!


The Future of RHI‘s at the LHC:

Dedicated HI experiment - ALICE

Two pp experiments with HI program:

ATLAS and CMS


Simple Expectations - Heavy Ion Physics at the LHC

QGP (fm/c)

(GeV/fm3)

T / Tc

tform (fm/c)

√sNN (GeV) factor 28

2-4

5

1.9

0.2

200

RHIC

≤ 2

3

1.1

1

17

LHCSPS

5500

0.1 shorter

3.0 - 4.2 hotter

15-60 denser

> 10longer-lived

Significant increase in hard scattering yields at LHC:

- jets & large pT processes

- bb (LHC ) ~ 100 bb (RHIC)

- cc (LHC) ~ 10 cc (RHIC)


Explaining the AdS/CFT Equivalence

Maldacena’s Conjecture

3) Strongly Coupled (Conformal) Gauge Field

Theories (CFT)

1) Weakly Coupled (classical) gravity in Anti-deSitter Space (AdS)

2)

Documents

Evidence for a Q u a r k - G l u o n Plasma in Relativistic Heavy Ion Collisions