# Presentation: 401158

## RECENT RESULTS FROM BRAHMS

- Ramiro Debbe
- Physics Department
- Brookhaven National Laboratory

**RECENT RESULTS FROM BRAHMS**
-      **CIPANP 2003 New York May 2003**

- R. Debbe CIPANP 2003

## Introduction 

- We report comprehensive results of our analysis of the 200 GeV Au-Au data.
- This work concentrates on the 5% most central events.
- This work is based on the PhD theses of two NBI students:
- Djamel Ouerdane and Peter Christiansen
- All results presented today are **PRELIMINARY****.**

- R. Debbe CIPANP 2003

## Introduction cont.

**BRAHMS** is one of the five **RHIC** experiments. BRAHMS is designed to study the bulk properties of the collisions. We measure charged particle production in a wide rapidity range and transverse momenta extending up to ~5 GeV/c.
- These measurements are done with two  conventional spectrometers with small acceptance.
- We put special emphasis on our Particle Identification capabilities with a combination of Time of Flight and Čerenkov detectors.

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## Slide 4

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## Particle Identification

**Mid-rapidity Spectrometer**

**Forward Spectrometer**

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## d2n/pTdpT=A(p0+pT)-n

**d****2****n/p****T****dp****T****=A(p****0****+p****T****)****-n**

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## Slide 7

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## Slide 8

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## Slide 9

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## Slide 10

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## 

**Mean Transverse momentum**

**K**

**P**

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## Net Charge as function of y

- The net charge is fitted to :
- A cosh(y/b)
- D. Kharzeev PLB378(96)238
- 2=7.4/6
- A = 8.5 0.3
- b = 2.4 0.1
- Total number of protons in  y range: -3, 3

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## Anti-proton/pion at y=0

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## Anti-proton/pion at y~3

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## RHIC data is “far” from the “resonance gas” ; the contribution of rescattering to the shape of distributions is small. Transverse flow is the dominant feature

- RHIC data is “far” from the “resonance gas” ; the contribution of rescattering to the shape of distributions is small. **Transverse flow is the dominant feature**

- R. Debbe CIPANP 2003

## Thermal source with transverse flow

- A change to a Boltzman distrib. Integration over y and phi produce the following function:

- Changing to a Boltzman distrib. And integrating over y and  produces the following function to fit the measured spectra. (T = tanh)

- Distributions of particles are assimilated to the counting of particles traversing a hyper-surface  beyond which the system decouples

- R. Debbe CIPANP 2003

## Transverse flow at y=0

******2****/****NDF ****= 6.7**
******T**** = 0.53**
**T  = 138. MeV**

**Transverse flow at y=0**

**Fits ********+**** ********-**** ****K****+ ****P  Pbar. Errors are statistical**

-  pions
-  kaons
-  proton

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## Transverse flow at y~3

**Transverse flow at y~3**

******2****/****NDF ****= 1.2**
******T**** = 0.42**
**T  = 140  MeV**

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## Transverse flow at y=3

- The presence  of transverse flow in the system is most evident in the shape of the proton distribution.
- Even though a fit to a thermal source with transverse flow does not fail, the comparison  to the distribution at y=0 supports the assertion that **transverse flow is much reduced at y=3.**

- R. Debbe CIPANP 2003

## Summary

-  BRAHMS measurements in a range of up to 2 units of rapidity around 0, are **consistent with a thermalized system that exhibits  strong transverse flow (********≥0.5). **
** **Hadronization at RHIC happens when the system is dilute. Secondary interaction (pion wind ) are not the main contributors to the shape of the distributions.
-  Transverse flow is reduced at y~3.

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## BRAHMS Coverage

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## Slide 22

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## Transverse flow at y~1

******2****/****NDF ****= 6.6**
******T**** = 0.57**
**T  = 115 MeV**

**Transverse flow at y~1**

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## Transverse flow at y~2

******2****/****NDF ****= 56/30**
******T**** = 0.47**
**T  = 135. MeV**

**Transverse flow at y~2**

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## K+p/pion

**Y = 0**

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## K+P/ at y=3

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