# Presentation: 786422

## High PT Measurements with BRAHMS

- I.G. Bearden,
- Niels Bohr Institute
- For
- The BRAHMS collaboration

- BNL High Pt Colloquium

- 18. JUNI 2003

## The BRAHMS Collaboration

**I.G. Bearden****7****, D. Beavis****1****, C. Besliu****10****, Y. Blyakhman****6****, J.Brzychczyk****4****, B. Budick****6****,**
**H. Bøggild****7 ****,C. Chasman****1****, C. H. Christensen****7****, P. Christiansen****7****,J.Cibor****4****, R.Debbe****1****,**
**J. J. Gaardhøje****7****,****M. Germinario****7**** ****,****K. Grotowski****4**** , K. Hagel****8****, O. Hansen****7****, **
** ****H. Ito****11****, E. Jacobsen****7****, A. Jipa****10****, J. I. Jordre****10****, F. Jundt****2,**** **
**C.E.Jørgensen****7****, E. J. Kim****5****, T. Kozik****3****, T.M.Larsen****12****, J. H. Lee****1****, Y. K.Lee****5****, **
**G. Løvhøjden****2****, Z. Majka****3****, A. Makeev****8****, B. McBreen****1****, M. Murray****8****, J. Natowitz****8****, **
**B. Neuman****11****,B.S.Nielsen****7****, K. Olchanski****1****, D. Ouerdane****7****, R.Planeta****4****, F. Rami****2****, **
**D. Roehrich****9****,  B. H. Samset****12****, S. J. Sanders****11****, I. S. Sgura****10****, R.A.Sheetz****1,**** Z.Sosin****3****, **
**P. Staszel****7****, T.S. Tveter****12****, F.Videbæk****1****, R. Wada****8**** and A.Wieloch****3****,Z. Yin****9**
**1****Brookhaven National Laboratory, USA, ****2****IReS and  Université Louis Pasteur, Strasbourg, France**
**3****Jagiellonian University, Cracow, Poland, ****4****Institute of Nuclear Physics, Cracow, Poland**
**5****Johns Hopkins University, Baltimore, USA,**** 6****New York University, USA**
**7****Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark**
**8****Texas A&M University, College Station. USA, ****9****University of Bergen, Norway **
**10****University of Bucharest, Ro****mania,**** ****11****University of Kansas, Lawrence,USA   **
**12**** University of Oslo Norway**** **

- - 52 people from 12 institutions-

- BNL High Pt Colloquium

- 18. JUNI 2003

## The BRAHMS Experiment

- BNL High Pt Colloquium

- 18. JUNI 2003

## Au+Au Charged Hadron Spectra   

- Au+Au Charged Hadron Spectra

****=0

****~2

- BNL High Pt Colloquium

- 18. JUNI 2003

## d+Au Charged Hadron Spectra 

- 200GeV (BRAHMS preliminary)

****=0

- BNL High Pt Colloquium

- 18. JUNI 2003

## Nuclear Modification Factor

- Hard processes (incoherent)
-  scaling with the number of
-     binary collisions Nbin.

- The nuclear modification factor:

- Glauber calculation

|  |   Nbinary |
| --- | --- |
| Au+Au 0-10% | 892 |
|          10-20%  | 570 |
|          20-40%  | 281 |
|          40-60% | 81 |
| dAu     MinBias | 7.3 |

- BNL High Pt Colloquium

- 18. JUNI 2003

## How does it look at lower energies?

- Modification quantified
- by:  ******pA****=A********(****pT****)**** ******** ****pp**

**Central Pb+Pb (SPS):**

- High pT enhancement explained by initial state multiple
- scattering (“Cronin effect”) and (for SPS) transverse flow...

- BNL High Pt Colloquium

- 18. JUNI 2003

## Reference Spectrum

-  UA1 acceptance **|********|** < 2.5
-  STAR acceptance **|********|** < 0.5

-  BRAHMS acceptance:
-        (this analysis)
-   MRS:  **|********|** < 0.15
-    FS:   2.0 <****< 2.2

-  scale UA1 results to **BRAHMS**
-     acceptance.

- (sNN=200 GeV)

- BNL High Pt Colloquium

- 18. JUNI 2003

## Nuclear Modification =0 

- Central to “peripheral”
- (cancellation of systematic errors)

- Au+Au at 200GeV

-  Large high pT suppression
-   for central collisions
-  Not seen for “peripheral”
-   collisions

- BNL High Pt Colloquium

- 18. JUNI 2003

## Nuclear Modification =2 

- Au+Au at 200GeV

- Central to “peripheral”
- (cancellation of systematic errors)

-  Qualitatively  same behaviour as
-   seen at ****=0

- BNL High Pt Colloquium

- 18. JUNI 2003

## Comparison =0 to =2

- Comparison ****=0 to ****=2

****=0

****=2

****=0

****=2

- BNL High Pt Colloquium

- 18. JUNI 2003

## d+Au Nuclear Modification  =0

- High pT enhancement
- observed in d+Au collisions
- at sNN=200 GeV.

- Comparing Au+Au to d+Au
-  strong effect of
-     dense nuclear medium

- BNL High Pt Colloquium

- 18. JUNI 2003

## Summary

-    Strong high pT suppression
-         in central collisions
-    Suppression not observed in semi-peripheral
-        collision (40-60%)
**Strong effect of dense medium!**
-  **Au+Au at ********s****NN****=200 GeV, ************2:**
-    Similar behaviour as observed at =0
-         (calls for additional theoretical work)
**Medium extends to ********=2!**
-  **d+Au at ********s****NN****=200 GeV, ********=0:**
-    “Cronin” like enhancement
**Medium not present in d+Au!**

- BNL High Pt Colloquium

- 18. JUNI 2003