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Searching Evidence for the Color Glass Condensate at RHIC. New Discoveries at RHIC BNL, May 14-15, 2004. J.-P. Blaizot and F. Gelis, SPhT, CEA Saclay and CNRS. Quantum ChromoDynamics. Non linear effects become important when. Gluon saturation

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Searching Evidence for the

Color Glass Condensate

at RHIC

New Discoveries at RHIC

BNL, May 14-15, 2004

J.-P. Blaizot and F. Gelis, SPhT, CEA Saclay and CNRS


QuantumChromoDynamics

Non linear effects become important when


Gluon saturation

a regime with weak coupling, many

cooperating degrees of freedom, strong fields.

Non linear effects important when

Saturation scale

Gribov, Levin, Ryskin 83

Mueller, Qiu 86


High density partonic systems

Large occupation

numbers

Classical fields


The saturation scale

From fit to DIS (HERA)

In a nucleus

The conditions in the central rapidity of a nucleus-nucleus collision

at RHIC are similar to those at 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


NON LINEAR EVOLUTION EQUATIONS

BALITSKY-KOVCHEGOV EQUATION

COLOR GLASS CONDENSATE

AND JIMWLK(*) EQUATION

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




Geometrical scaling

(Golec-Biernat,Kwiecinski,Stasto)


Numerical solution of the BK equation + DGLAP corrections

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





PHOBOS Central Au+Au (200 GeV)

600

1200

Compilation by K. Eskola

Total multiplicities


PHOBOS, PRL 87

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



« Limiting fragmentation »

PHOBOS, PRL 91

Interpretation in the color glass picture:

J. Jalilian-Marian, nucl-th/0212018





y

0

0.05

0.1

0.2

0.4

0.6

1

1.4

2

Albacete et al, hep-ph/0307179

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






- Saturation picture (color glass condensate) does provide a successful phenomenology, both at RHIC and at HERA.

- Saturation manifests itself at lower energy in nucleus-nucleus collisions than in proton-proton collisions

- Color glass only provides initial conditions. Because of final state interactions, AA collisions do not allow for direct tests.

- dA are much better. Going to forward rapidity one gets a chance to « see » evolution of parton densities.

- Phenomena should be more visible at the LHC


Why is it important to search for the color glass condensate ?

  • Saturation is a genuine, characteristic, QCD effect

- Important to get a complete control of the initial conditions

  • May well turn into an essential piece in the chain of

  • arguments leading to the identification of the quark-gluon

  • plasma


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