The study of hot and dense matter at RHIC

RIKEN, TokyoDecember 6, 2004

Jean-Paul Blaizot, CNRS and ECT*

QCD and asymptotic freedom

Matter is simple at high density/high temperature- early universe- deconfined quark-gluon plasma

Interactions beween « strongly » interacting particles arecalculable

(S. Bethke, hep-ex/0211012)

QCD Interactions Weaken at High Energy

Weak coupling, few particles

Factorisation theorems

Accurate calculations can be done

Perturbative QCD

What can we predict from pQCD?

Initial production of hard probes (jets, heavy quarks, etc.)

Deviations from predictions signal new physics (e.g., J/Psisuppression (?), jet quenching, heavy quark propagation,etc.)

In A-A collisions, binary scaling

Initial wave function

Elementary cross-section

Fragmentation function

Factorization theorems of pQCD

(PHENIX, hep-ex/0304038)

Pi0 production in p-p

(nucl-ex/0409032)

Direct photons at RHIC

At high temperature and/or high density matter is « simple »

But transition from hadronic phase to the asymptotic quark-gluon plasma is not

Matter at high temperature is like radiation

(from F. Karsch, hep-lat/0106019)

Weakly interacting quasiparticles

T

µB

Hadronic matter

Quark-Gluon Plasma

Nuclei

Colour superconductor

The QCD phase diagram

Fodor and Katz, JHEP 0404 (’04) 050

Kazmarek et al hep-lat/0312015

Heavy quark free energy

Laermann et al, NPB42(1995)

Color averaged potential

Expected « signatures » of the QGP

- Stangeness enhancement- J/Psi suppression- Direct signals of phase transiton (thresholdphenomena, characteristic collective behaviours)- Jet energy loss- Thermal radiation- Etc.

Phenomena related to all of those have been observed

From SPS

to RHICNA35

Experimental discoveriesMany evidences for non trivial phenomena

Large energy density

Collective behaviour

Suppression of charmonium bound states

Jet quenching and strong « final state » interactions

Hints of gluon saturation

And much more…

Statistical/chemical equilibrium at freeze-out

Moderate increase of multiplicity with beam energy

From PhenixWhite paper

Bjorken energy density

Matter at « freeze-out »

well described bystatistical picture

(STAR white paper)

Statistical/chemical equilibrium

Collective flow of produced matterProduced particles flow preferentiallyin the reaction plane

(J.-Y. Ollitrault, 1992)

€

εx =y 2 − x 2

y 2 + x 2

€

εp =Txx −Tyy

T xx + Tyy(P.F.Kolb, J. Sollfrank and U. Heinz, PRC 62 (2000) 054909)

Elliptic flow

(Quark-Matter 02) (Phenix white paper)

q

q

pp

AuAubinaryAuAuAA Yield

NYieldR

/ 〉〈=

Au-Au nucl-ex/0304022

Jet production in matter

(PHENIX, nucl-ex/0401001)

Control experiment: d-AU

STAR: Phys.Rev.Lett.91:072304,2003

J/ψ SUPPRESSION IN NUCLEAR COLLISIONS

(from N. Willis)

Expected

Measured

Evidence for the formation of the quark-gluon plasma (?)

NA50 Experiment

Have we found the quark-gluonplasma at RHIC?

Perhaps this is not such a well-posed question …

« …a strongly interacting medium is created with extremely high energy density, whose description in terms of hadronic degrees of freedom is inappropriate… » (PHOBOS white paper)

RHIC 2004

« Are we there yet? » (STAR white paper)

« …a new state of matter has beencreated…at energy densities whichexceed by more than a factor 20 that ofnormal nuclear matter….featuresmany of the characteristics of thetheoretically predicted quark-gluonplasma. » (Heinz & Jacob)

SPS 2000

(Indirect) evidences for collective behaviour at thepartonic level

Evidence for short thermalization time, low viscosity, strong interaction at early times produced matter is not an ideal quark-gluon plasma

No sharp transition in any observable as a function of energy

At the SPS, many phenomena obscured by strong final state interactions, particle production dominated by soft physics

Initial state plays a more important role at RHIC

Phenomena more spectacular at RHIC, interpretation reliesmore on QCD

Quantum ChromoDynamics

Non linear effects become important when

Gluon saturation a regime with weak coupling, many cooperating degrees of freedom, strong fields.

Saturation scale

Non linear effects important when

Gribov, Levin, Ryskin 83Mueller, Qiu 86

High density partonic systems

Large occupation numbers

Classical fields

The saturation scale

In a nucleus

The conditions in the central rapidity of a nucleus-nucleus collision at RHIC are similar to those at HERA

From fit to DIS (HERA)

Early stages of a nucleus-nucleus collision

Partons set free have typical tranverse momenta

They are set free at (proper) time

At that time

(J.-P. B., A. Mueller, 87)Momentum distributions

COLOR GLASS CONDENSATE AND JIMWLK(*) EQUATION

(*) Jalilian-Marian, Iancu, McLerran, Weigert, Leonidov, Kovner

NON LINEAR EVOLUTION EQUATIONS

BALITSKY-KOVCHEGOV EQUATION

EXPERIMENTAL TESTS

DEEP INELASTIC SCATTERING

(Golec-Biernat,Kwiecinski,Stasto)

Geometrical scaling

(Gotsman, Levin, Lublinsky, Maor hep-ph/0209074)

Numerical solution of the BK equation + DGLAP corrections

(Iancu, Itakura, Munier hep-ph/0310338)

RHIC

PARTICLE MULTIPLICITIES

600 1200

PHOBOS Central Au+Au (200 GeV)

Compilation by K. Eskola

Total multiplicities

(Kharzeev, Levin, Nardi)

Kharzeev & Levin, Phys. Lett. B523 (2001) 79

PHOBOS, PRL 87

(Kharzeev, Levin, Nardi hep-ph/0212316)

« Limiting fragmentation »

PHOBOS, PRL 91

Interpretation in the color glass picture: J. Jalilian-Marian, nucl-th/0212018

SPECTRA

(Kharzeev, Kovchegov, Tuchin, hep-ph/0405045)

RATIOS OF SPECTRA

Albacete et al, hep-ph/0307179

y0

0.05

0.1

0.2

0.4

0.6

1

1.4

2

(Related analytical work by Iancu, Itakura, Triantafyllopoulos hep-ph/0403103)

(J.-P. B, F. Gelis, R. Venugopalan, hep-ph/0402256)

(J.-P. B, F. Gelis, R. Venugopalan, hep-ph/0402256)

(Kharzeev, Kovchegov, Tuchin, hep-ph/0405045)

(Kharzeev, Kovchegov, Tuchin, hep-ph/0405045)

SUMMARY- Vast body of precise data, provide detailed information oncollision dynamics, suggesting a « standard scenario » ofnucleus-nucleus collisions. However, no unique frameworkaccounts for all the data. Puzzles remain- Strongly interacting matter is produced in high energynucleus-nucleus collisions- Many evidences that partonic degrees of freedom play animportant role in the collision dynamics at RHIC, while SPSpysics is largely dominated by « soft » physics- Early stages of the collisions, and hence « intial state effects »play an important role at RHIC (and will be more so at LHC).Hints of saturation (color glass condensate) may be alreadypresent at RHIC- QCD has become a central reference in the analysis of the data