Kent State University, March 8, 2007 1 The QGP comes of age The Quark-Gluon Plasma Comes of Age Peter Jacobs, Lawrence Berkeley National Laboratory

1Kent State University,March 8, 2007 The QGP comes of age

The Quark-Gluon Plasma Comes of Age

Peter Jacobs, Lawrence Berkeley National Laboratory


• Brief tour of QCD

• QCD Matter and its phase transitions

• Quantitative measurements of QCD Matter: jet quenching and shear viscosity

• What’s the deal with string theory and heavy ion collisions?

• Future directions at RHIC and the LHC

Outline


Quantum Chromodynamics (QCD)

,1

1( )

2 4

f

a a

na

QCDa

af

Ai g FL m F

fieldsquark

fieldsgluon

ψ

Aa CBABCAAA AAgfAAF

The Strong Interaction in the Standard Model

e

u s b

d c t

e

Quarks

Leptons

g (gluon):Strong interaction

W, Z boson:Weak interaction

(photon): EM interaction

strong coupling constant


Running of the coupling in relativistic field theory

Q2

Small momentum transfer Q2 large distance scales

Large momentum transfer Q2 small distance scales

Virtual pairs (loops) screen bare interaction momentum-dependent interaction strength


Running of the coupling: QED vs QCD

Larger |Q2| (smaller distance) larger coupling • similar to screening of charge in di-electric material

QED:

2

2

22

||log

3

111

Q

Q

negative

QCD:

2

2

22

||log

12

21111

QnN

Qflavorcolor

SS

=+(33-12)/12 = positive!

Larger |Q2| (smaller distance) smaller coupling

And that makes a huge difference!

4

2g


Running of S

0.2 fm 0.02 fm 0.002 fm

Q Q

Confinement

Asymptotic Freedom

coneR

Gross Politzer Wilczek


QCD is a precise theory at large Q2

Inclusive jet production Deep inelastic scattering

small x

large x

x = partonic momentum fraction


Phase Diagram of Water

Not directly calculable from the QED Lagrangian:complex emergent features

Pressure


Phase Diagram of QCD Matter

high T ~ high Q2 ~ deconfinement


Early Universe

COBE and WMAP: universe is highly equilibrated relics of early phase transitions are difficult to see


Lattice QCD at Finite Temperature

F. Karsch, hep-ph/0103314

Critical energy density: 4)26( CC T

TC ~ 175 MeVC ~ 1 GeV/fm3

Ideal gas (Stefan-Boltzmann limit)

Not an ideal gas even at 3TC (will return to this point)


STAR

The Relativistic Heavy Ion Collider


Calibrated in p+p and p/d+A

Calculable final state medium effects (pQCD-based)

Hard probes of QCD matter

Calculable interactions of energetic partons with the medium calibrated, penetrating tomographic probes


Testing pQCD in p+p at RHIC

Good agreement with NLO pQCD pQCD should be broadly applicable

Inclusive jets

B.I. Abelev et al., PRL 97, 252001 (2006)


Jet quenching: hadron suppression

-

Energy loss softening of fragmentation suppression of leading hadron yield

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

Binary collision scaling p+p reference


Jet quenching I: hadrons are suppressed, photons are not

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

Jets (color-charged)

Photons (color-neutral)


Jet structure via hadron correlationsp+p dijet

Full jet reconstruction in the heavy ion environment is difficult probe jet structure via dihadron correlations

trigger

Phys Rev Lett 90, 082302


Jet quenching II: recoiling jets are strongly modified

4< pTtrig < 6 GeV

trigger

recoil

?

STAR, Phys Rev Lett 91, 072304

pTassoc > 2 GeV

Hard recoil hadrons

cos()

pTassoc > 0.15 GeV

STAR, Phys Rev Lett 95, 152301

All recoil hadrons

Striking qualitative effects: conclusive evidence for large partonic energy loss in dense matter


Radiative energy loss in QCD

CS

coherent

LPM Nq

dzd

dI

ldzd

dI ˆHeitlerBethe

2ˆ~ˆ~ LqLqdzd

dIddzE SCS

LPML

med

C

cformation Lt

BDMPS model: multiple soft collisions in a medium of static color charges

E independent of parton energy (finite kinematics E~log(E))E L2 due to interference effects (expanding medium E~L)

Medium-induced gluon radiation spectrum:

Total medium-induced energy loss:

2

2

22ˆ

qd

dqqdq mediumTransport coefficient:

Baier, Schiff and Zakharov, AnnRevNuclPartSci 50, 37 (2000)


qhat from single hadron suppression

densitymattercoldx30~GeV155~ˆ 2 fmq

Eskola et al ‘04


What does measure?q̂

LqxxGN

Nq medium

C

CS ˆ,1

4ˆ

2

2

Equilibrated gluon gas:number density ~T3

energy density ~T4

43

ˆ cq

qhat+modelling energy density

• pQCD result: c~2 (S? quark dof? …)• sQGP (multiplicities+hydro): c~10

Model uncertainties

R. Baier, Nucl Phys A715, 209c

Hadronic matter

Deconfined matter

~RHIC data


The limitations of hadron suppression

?

q̂Core of fireball is opaque to jets

RAA provides only poor upper constraint on

Eskola et al. ‘04

Look for more sensitive observables…


Dihadron correlations at higher pT

Recoil jet clearly seen above background but at suppressed ratedifferential measurement of`E upper bound on qhat

trigger

recoil

?

pTtrigger>8 GeV/c

Yie

ld p

er tr

igge

r

STAR, nucl-ex/0604018


STAR preliminary

T. Renk, hep-ph/0602045

High pT hadrons: detailed dynamical calculations

Trigger direction

Different geometrical biases underly trigger and recoil distributions

~75% of recoils due to non-interacting jets

All bremsstrahlung models: discrete term


Zhang, Owens, Wang and Wang nucl-th/0701045

from single and di-hadon suppression

fmq 2GeV3.08.2~ˆ

Consistent minima for two independent measurements

q̂


Main new result in this talk: the first accurate* measurement of a transport property of QCD Matter

pathfreemean

transfermomentum 22

q

QCD Matter at T~200 MeV: fmq 2GeV3.08.2~ˆ

* excluding theoretical uncertainties


Testing radiative energy loss: heavy quarks• In vacuum, gluon radiation suppressed at < mQ/EQ

• “dead cone” effect: b, c quarks fragment hard into heavy mesons

QDokshitzer, Khoze, Troyan, JPG 17 (1991) 1602.Dokshitzer and Kharzeev, PLB 519 (2001) 199.

Dead cone also implies lower heavy quark energy loss in matter: radiation cannot outrun the probe (Dokshitzer-Kharzeev, 2001)

1

1

dd

d

d2

2

2

Q

Q

LIGHT

HEAVY

E

m

II

heirarchy of jet energy loss: gluon > u,d,s > charm > bottom


Heavy quark suppression via b,c→e+X

Standard radiative energy loss

ignore b-quark contribution

Heavy quarks are “over-suppressed” missing mechanisms? Energy loss via elastic scattering?


Heavy quark suppression cont’dValidation of radiative energy loss theory requires resolution of heavy quark suppression puzzle

Need new detectors to explicitly separate b and c contributions:

inner trackers for PHENIX and STAR

important Kent State contributions…


Collective Flow of QCD Matter

xy z

Initial spatial anisotropy

py

px

Final momentum anisotropy

x

y

p

patan

22

22

xy

xy

22

22

2

yx

yx

pp

ppv

Reaction plane defined by “soft” (low pT) particles

Elliptic flow )](2cos[21 2 Rvd

dN


Relativistic (Perfect) Hydrodynamics

1 fm/cth Good agreement requires thermalization at time

Heinz ‘04

Mass hierarchy vs momentum is characteristic of common velocity distribution

Heavy particles

Light particles0viscosityshear

0

T


mfpLA

F v~;v

Properties are counter-intuitive:

Weak coupling• small cross section, long mean free path large viscosity

Strong coupling• large cross section, small mean free path small viscosity

Shear viscosity in fluids

→0: strongly coupled (perfect) fluid→: weakly coupled (ideal) gas (!)


How perfect a fluid is QCD Matter?

/ 0.1s Constraint on shear viscosity: finite not excluded

Qualitatively, is “small”Quantitative measurement requires more detailed modeling and data

sTS

3

4

Teaney ‘03

T. Hirano et al., nucl-th/0701075

vary initial matter distribution

finite


Black holes and gauge theory via theAdS/CFT correspondence

Color Screening

cc

Maldacena ’98:

high temperature strongly-coupled gauge theory in 3+1 dimensions

classical string theory in vicinity of black hole in 4+1 dimensions

Conjecture: hidden within every non-Abelian gauge theory, even within the weak and strong nuclear interactions, is a theory of quantum gravity.(Horowitz and Polchinski, gr-qc/0602037 )Warning: I am not a string theorist.


Shear viscosity and entropy in AdS/CFT/s of a black hole (M. Natsuume, hep-ph/0700120)

1.0~4 Bks

Universal result: gauge theory plasmas with gravity duals have a universal low value of /s at strong (‘t Hooft) coupling

Kovtun, Son and Starinets (KSS), PRL 94, 111601

Compare RHIC elliptic flow+hydro: /s~0.1

AreaBH

0lim

Shear visc. ~ cross section:

BBH kG

AreaS

4

Beckenstein entropy:


Spectral Properties of Hot QCD

Nakamura & Sakai, hep-lat/0510100

T/Tc

/spQCD

AdS/CFT

Shear viscosity: Lattice QCD vs AdS/CFT

Lattice: quenched approximation (no quarks)

Numerical agreement!


Jet quenching in AdS/CFT

Friess et al., hep-th/0607022

Hot gauge theory lives on boundary

Heavy quark is end of string on boundary

String provides drag (energy loss)

Can also calculate dynamical processes…

Black-hole horizon


Jet quenching: pQCD vs AdS/CFT

MeV300at94.0~

38ˆ

2322 T

fm

GeVTNq colorSpQCD

MeV300at5.4~ˆ

23

45

43

/

23

Tfm

GeVTNq colorSYMCFTAdS

Weak-coupling pQCD (Baier et al.):

Strong-coupling =4 SYM (Liu, Rjagopal and Wiedemann):

NOT proportional to NC2 ~ entropy density

Proportional to NC2 ~ entropy density

Recall fmqdata2GeV5.2~ˆ Rough numerical

agreement


String theory and hot QCD: commentsAt first sight the string theory connection looks unlikely to succeed. The gauge theories that have known gravity duals are not QCD:

• wrong degrees of freedom, infinite number of colors • supersymmetric• strong coupling limit• conformal theory (no running of the coupling)• no confinement or chiral symmetry

But some of these can be relaxed towards QCD (e.g. d.o.f, conformality)

But also, analogy to condensed matter physics: metals have widely differing structure yet have essential common features

The AdS/CFT correspondence may teach us about the emergent features of QCD-like theories (thermodynamics, transport properties,…)


The definitive connection of gauge theories to black hole physics would be a development of the first rank in importance!

Numerical agreements with data and Lattice QCD are provocative but not proofs of validity

For rigorous science need hard, testable predictions:

e.g. momentum dependence of J/ suppression (Liu, Rajagopal, Wiedemann)

Stay tuned!

String Theory summary cont’d


The New Yorker, Jan. 7 2007


mid-late 2007: commission 14 TeV p+pend 2008: first long 5.5 TeV Pb+Pb runheavy ion running: 4 physics weeks/year

Large Hadron Collider at CERN

ALICE

ATLAS

CMS


Jet quenching at the LHC

Pb+Pb at 5.5 TeV:• First ion collisions 2008• qualitatively new probes

enormous reach in jet energy

P. Jacobs and M. van LeeuwenNucl. Phys A774, 237 (2006)


Jets and hadrons at RHIC II

B.I. Abelev et al., PRL 97, 252001 (2006)

RHIC II (x 10 luminosity upgrade): also has significant kinematic reach (jets to ~60-70 GeV)


What is interesting about high ET jetsat RHIC II and LHC?

Precision QCD: the evolution of nucleon structure with Q2

(= resolution of the probe)

High ET jets at LHC and RHIC may provide similarly precise probes of hot QCD matter


ALICEHMPID

Muon Arm

TRD

PHOS

PMD

ITS

TOF

TPCSize: 16 x 26 meters

Weight: 10,000 tons

EMCal



U.S. Contribution to ALICE: EMCal a large electromagnetic calorimeter

Approved by LHCC 9/28/0610+1/2+1/2=11 super-modules8 SM from US3 SM from France, Italy

US Total Project Cost: $13.3M

CD-2/3 expected summer ‘07

Enables jet measurements in ALICE


Benchmark observable: modified fragmentation function

• MLLA: good description of vacuum fragmentation (basis of PYTHIA)• introduce medium effects at parton splitting Borghini and Wiedemann, hep-ph/0506218

Jet quenching fragmentation strongly modified at pT

hadron~1-5 GeV

=ln(EJet/phadron)

pThadron~2 GeV

Jet quenching


ALICE+EMCal in one LHC year

Detailed measurements of change in jet structure due to energy loss

Large jet quenching effects, exquisite statistical sensitivity

The key physics issue: how does this distribution evolve with Q2 (ET)?


SummaryRHIC has failed: the initial expectation of an ideal gas plasma of non-interacting quarks and gluons has not been met.

Instead, something much more interesting has been found:

The QCD Matter generated in RHIC collisions is the most perfect fluid known.

Its dynamical transport properties are calculable from fundamental theory, perhaps including string theory. They are therefore at least as interesting as its thermodynamics properties.

Controlled, quantitative study of these properties is under way at RHIC II and the LHC.

Documents

Kent State University, March 8, 2007 1 The QGP comes of age The Quark-Gluon Plasma Comes of Age Peter Jacobs, Lawrence Berkeley National Laboratory