# Presentation: 530383

## Searching Evidence for the

-    Color Glass Condensate
-                at RHIC

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

- New Discoveries at RHIC
-   BNL, May 14-15, 2004

**Notes:**
Change in title. Importance of looking for evidence of the color glass. A rather well defined question. Major theoretical progress done over the last decadee. May turn out to be an essential step in identifying the quark-gluon plasma.

## Quantum ChromoDynamics

**Quantum**** ****ChromoDynamics**

**Non linear effects become important when**

**Notes:**
Try to understand how QCD works. None of the phenomena observed in nucleus-nucleus collisions would give us a hint about the existence of quarks and gluons (if experiments had been done before QCD).

## Gluon saturation 

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

- Saturation scale

- Non linear effects important when

- Gribov, Levin, Ryskin 83
- Mueller, 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**

## NON LINEAR EVOLUTION EQUATIONS

-          AND JIMWLK(*) EQUATION

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

- BALITSKY-KOVCHEGOV EQUATION

## Slide 8

## Slide 9

## Slide 10

## EXPERIMENTAL TESTS

## DEEP INELASTIC SCATTERING

## Geometrical scaling

- (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

## Total multiplicities 

**Total multiplicities**

## Slide 19

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

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

- PHOBOS, PRL 87

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

## « Limiting fragmentation »

**« 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

## Slide 26

##  y

- Albacete et al,  hep-ph/0307179

-  y
- 0
- 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)

## CONCLUSIONS AND OUTLOOK

## - 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**

**Notes:**
If saturation seen, direct evidence that gluons do play an essential role as active degrees of freedom in the early stage of the collision. We are all convinced that it is so, but we wold « see » it.