# Presentation: 806703

## Brahms: Forward Physics at RHIC

## The BRAHMS Collaboration

- I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J.Brzychczyk4, B. Budick6,
- H. Bøggild7 ,C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1,
- E. Enger12, J. J. Gaardhøje7, M. Germinario7 , K. Grotowski4, K. Hagel8, O. Hansen7,
- A.K. Holme12, H. Ito11, E. Jakobsen7, A. Jipa10, J. I. Jørdre10, F. Jundt2, C.E.Jørgensen7,
- R. Karabowicz4, T. Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5,
- G. Løvhøiden2, Z. Majka3, A. Makeev8, E. McBreen1, M. Mikkelsen12, M. Murray8, J. Natowitz8,
- B.S.Nielsen7, J. Norris11, K. Olchanski1, J. Olness1, D. Ouerdane7, R.Planeta4, F. Rami2,
- D. Roehrich9,  B. H. Samset12, D. Sandberg7, S. J. Sanders11, R.A.Sheetz1,
- Z.Sosin3, P. Staszel7, T.S. Tveter12, F.Videbæk1, R. Wada8, A.Wieloch3, and I. S. Zgura10
- 1Brookhaven National Laboratory, USA, 2IReS and  Université Louis Pasteur, Strasbourg, France
- 3Jagiellonian University, Cracow, Poland, 4Institute of Nuclear Physics, Cracow, Poland
- 5Johns Hopkins University, Baltimore, USA, 6New York University, USA
- 7Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark
- 8Texas A&M University, College Station. USA, 9University of Bergen, Norway
- 10University of Bucharest, Romania, 11University of Kansas, Lawrence,USA
- 12 University of Oslo Norway

## MRS

- 

- FOWARD
- 

- GLOBAL

## Global detectors

- BB : Provide vertex and start time for TOF (and forward multiplicity)

- MA : Provide multiplicity / centrality of collision

## BRAHMS Preliminary 

**BRAHMS Preliminary**** **

- 4630 ± 370 charged particles produced for 0-5 % central.
- 21 %  increase over 130 GeV
- dNch/dη (η=0) = 625 ± 55(syst.)
- 14% increase over 130 GeV.
- Phobos 200 GeV : PRL 88, 22302 :
- dNch/dη (η=0) = 650 ± 35(syst.)
- 200 GeV : Submitted to PRL
- (nucl-ex/0112001)
- 130 GeV : Phys. Lett. B 523, p. 227

**0-5%**** **

**5-10%**** **

**10-20%**** **

**20-30%**** **

**30-40%**** **

**40-50%**** **

## Comparison to scaled          and models

## dN/d vs. 

- BRAHMS
- Preliminary

## Charged Particle Mult.snn=130GeV

- BRAHMS. Phys Lett. B. 523 227 (2001)

## Limiting fragmentation: SPS=>RHIC

## dN/d vs Npart

- Kharzeev and Levin (nucl-th/0108006)
- Soft-Hard:
-     dN/d=(1-X) npp <Npart>/2
-               + X  npp <Ncoll>
-     <Ncoll>=1049, <Npart>=339, npp=2.43  =>dN/d=668 (with X=0.9)
- High Density QCD-saturation:
-   dN/dy =f(Npart,Qs2,,QCD,s,y)
-     with =0.3 from HERA data
-     => dN/d=620
-     (using dN/d=549ats=130GeV)

- 130: A= 1.24  0.08±0.2, B =0.12-+0.04-+0.06

- 200: A= 1.26  0.09±0.2 B =0.15-+0.04-+0.05

## Comparison to 

- Comparison to
- Kharzeev &Levin
- PLB523(2001)79
- High dens. QCD
- Gluon saturation
- (red dashed)
- AMPT
- Zhang et al.
- PRC61(2001)067901
- (blue dashed)

- Data symmetrized
- Error bars are
- Total = Sys. + Stat.

## dN(200GeV)/dN(130GeV)

- top 5%

- 5-10

- 40-50

- 30-40

- K&L solid line

- AMPT dashed line

## Ratios of particles and anti-particles at

- By looking at ratios of particles and anti-particles in the same spectrometer angular setting, from fields of opposite polarities the geometrical acceptance of the detector and efficiencies will tend to cancel out.
- We still have to take into account absorption of anti-protons and protons produced in the beampipe.

## Ring Imaging Cherenkov

## Rapidity dependence of ratios at               .

**BRAHMS Preliminary**** **

- (and feeddown)

## Ratios vs Pt and centrality

- BRAHMS Preliminary

- BRAHMS Preliminary

- No sign of Pt or centrality dependence

## Pbar/p increases slowly with √S

## We don’t yet understand baryon transport

- AMPT

##  √S dependence, towards matter/antimatter balance

- Protons

- Kaons

- Preliminary

## Estimate of net protons at midrapidity

## Summary First Au+Ausnn=130 ,200 GeV 

-         _RESULTS: 100+100_
- Nch (0-5%)  5000
- dN/d (y=0)  632. FWHM  7.5
- N(ch)  30 pr. participant-pair
- dN/d (y=0)   3.5/part. pair
- p-bar/p higher at y=0, similar at forward rapidity

- _RESULTS: 65+65_
- Nch (0-5%)  4000
- dN/d (y=0)  550. FWHM  7.2
- N(ch)  23 pr. participant-pair
- dN/d (y=0)   3 pr. part. Pair
- p-bar/ p vs y shows increased  but still incomplete transparency
- Midrapidity Plateau?
- y =0,0.7,2 : pbar/p  0.64, 0.66, 0.41 (±0.05 ± 0.06)
- Weak pt and centrality dependence
- Models inconsistent with data