Brahms: Forward Physics at RHIC

T1

MTPC1

T2

MTPC2

MRS: 90 deg

6.5 msr

FS: 6 deg

0.8 msr

Dipole Magnets

The BRAHMS CollaborationI.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, France3Jagiellonian University, Cracow, Poland, 4Institute of Nuclear Physics, Cracow, Poland

5Johns Hopkins University, Baltimore, USA, 6New York University, USA7Niels 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

Silicon Strips

Plastic Scintillator Tiles

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

MA : Provide multiplicity / centrality of collision

Multiplicity at from MA and BB200NNsBRAHMS 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 modelspp

data(UA5, Z. Phys. C 33, 1) : BRAHMS data shows 50% increase at η = 0

Models : Kharzeev and Levin (solid) and AMPT(dashed) describes the data well.

pp

pp

BRAHMS Preliminary

dN/d vs.

BRAHMSPreliminary

Charged Particle Mult.snn=130GeV

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

SPS

Limiting fragmentation: SPS=>RHIC

SPS Pb- Pb(NA49)

200 GeV top 5%

130 GeV top 5%

200 GeV 30-40%

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=549ats=130GeV)

Fit to dN /d = AN + BN :ch part coll

130: A= 1.24 0.08±0.2, B =0.12-+0.04-+0.06200: A= 1.26 0.09±0.2 B =0.15-+0.04-+0.05

Comparison to Kharzeev &LevinPLB523(2001)79High dens. QCD Gluon saturation (red dashed)AMPTZhang et al. PRC61(2001)067901(blue dashed)

Data symmetrizedError bars are Total = Sys. + Stat.

dN(200GeV)/dN(130GeV)

top 5% 5-10

40-5030-40

K&L solid lineAMPT dashed line

Ratios of particles and anti-particles at 200NNs

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

2

Rapidity dependence of ratios at .

)()(

)(

)(

)(

tp

p

pNpN

pN

pN

pN

)(

)()(

)(

)(

)(

Kppp

KNKN

KN

KN

KN

app

p

BRAHMS Preliminary

(and feeddown)

PRL 87, 2001 ▄

200NNs

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

* Assuming 14% more pbar (cf. dN/dη, BRAHMS sub to PRL dec.2001) and 0.75.

NNs 200 GeV (30) (23) (7)*

)(/)( pNpN

* NA49 QM99 & Phys. Rev. Lett. 82, 2471 (1999)

NNs 17 GeV 31 5 26*

* PHENIX nucl-ex/0112006

NNs 130 GeV 29 20 9*

)()(

)(

)(

)(

otherpair

pair

pNpN

pN

pN

pN

N(p) )pN( )pN( -N(p)CM Energy

Summary

First Au+Ausnn=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