# Presentation: 034882

##        Probing the Color Glass Condensate 

**       ****Probing the ****Color ****Glass**** ****Condensate**** **
**         ****in d-A  collisions at RHIC****                    ****DNP 2002 Fall Meeting**                                        **Oct 9-12, 2002****                          ****East Lansing**** ****Michigan**

**Ramiro Debbe**
**Physics Department**
**Brookhaven National Laboratory**

- DNP 2002 MSU

## Motivation

- The Color Glass Condensate is postulated as a description of the **initial state** of high energy collisions where most of the particle production is driven by the “small x modes in the

- CGC predicts a saturation in the gluon density at        **Q****sat****2**** ~ 1 -2 GeV****2**** **

- nuclear wave function”
- Particle production is mainly related to the gluon distributions.

- DNP 2002 MSU

## BRAHMS can reach very small values of x in the Au gluon distributions:

- Were A is d and B is Au. Energy and momentum conservation
-                 xL = xa - xb
-                         **k****a**** + k****b**** = k**
-                 xaxb = MT2/s
- A solution to this system is:
-     xa = (MT/√s) ey
-       xb = (MT/√s) e-y
- Where y is the rapidity of the (xL, **k**) system

- DNP 2002 MSU

## Even though the (xL, k) has to hadronize or may reinteract

- I make a one-to-one correspondence with the particles we detect.

- There are several publications with descriptions of how the onset of CGC would modify the final state distributions in PT  or multiplicity densities.

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## J. T. Lenaghan and K. Tuominen hep-ph/0208007

**Y = 0**

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## Q2s(s,y) = Q2s(s,y=0) ey

- Q2s(s,y) = Q2s(s,y=0) ey

- Figures extracted from one of L. McLerran lectures.

- DNP 2002 MSU

## Event characterization

- We will rely on the multiplicity of charged particles within -2< <2
- We estimate that we can make at least two to three cuts to characterize the collision.

****

- DNP 2002 MSU

## Acceptance

- Charged pions in the forward spectrometer
- 2.3 <  < 6
- And
- 2 < p < 25 GeV/c

**p****T**

**x****2**

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## Pions at 14<<30

-             **0.5 < p < 25 GeV/c**

**p****T**

**x****2**

- DNP 2002 MSU

## Protons in the Forward spectrometer

- 2.3<<14
- 1 < p < 32 GeV/c

**p****t**

**x****2**

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## BRAHMS Acceptance

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## Rate estimates

| pT [GeV/c] | Protons (106 colls) |
| --- | --- |
| 2 | 0.15 x 106 |
| 4 | 0.18 x 103 |
| 6 | 0.24 |
| 7 | 0.008 |

- At =3,  = 3.6 dN/dy = 3.5 there will be 0.004 charged particles within the FS acceptance (=3 pT>800MeV/c). If I use the most optimistic estimate for the luminosity (80 K interactions/sec). I have 350 charged part/sec (89% charged pions and 11% protons)

- If we want 10% stat. error at 6 GeV/c we would need to collect 400 million collisions:
-       ~ 1.5 hours

- DNP 2002 MSU

## Rate estimates cont.

| pT [GeV/c] |  pions (106 events) |
| --- | --- |
| 2 | 2.5 x 104 |
| 4 | 1 |
| 6 | 5 x 10-5 |

- For pions a better region may be  ~12 (=2.2), dN /dy ~7
- 0.0014 pions per event in FS acceptance (=3.8 pT>800**MeV/c**).
- We have 110 events/sec with tracks in FS.
- We will need ~100 million collisions to reach 10% stat. error at 4 GeV/c. ( 1/2 hour)

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## Slide 14

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## Slide 15

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## Summary

**BRAHMS** will study inclusive distributions at high rapidities ( up to y~3 for protons and y~ 2 for pions)
- We will try to reach high pT values (> 4 GeV/c)
- Together with our **p-p** measurement we should be able to contribute to the discussion about the onset of saturation in the initial state at RHIC energies

- DNP 2002 MSU