Brahms: Forward Physics at RHIC

Brahms: Forward Physics at RHIC T2 FS: 6 deg T1 Dipole Magnets MRS: 90 deg 6.5 msr MTPC1 MTPC2

0.8 msr The BRAHMS Collaboration I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J.Brzychczyk4, B. Budick6, H. Bggild7 ,C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1, E. Enger12, J. J. Gaardhje7, M. Germinario7 , K. Grotowski4, K. Hagel8, O. Hansen7, A.K. Holme12, H. Ito11, E. Jakobsen7, A. Jipa10, J. I. Jrdre10, F. Jundt2, C.E.Jrgensen7, R. Karabowicz4, T. Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5, G. Lvhiden2, 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.Videbk1, R. Wada8, A.Wieloch3, and I. S. Zgura10 1

Brookhaven National Laboratory, USA, 2IReS and Universit Louis Pasteur, Strasbourg, France 3 Jagiellonian University, Cracow, Poland, 4Institute of Nuclear Physics, Cracow, Poland 5 Johns Hopkins University, Baltimore, USA, 6New York University, USA 7 Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark 8 Texas A&M University, College Station. USA, 9University of Bergen, Norway 10 University of Bucharest, Romania, 11University of Kansas, Lawrence,USA 12 University of Oslo Norway

FOWARD GLOBAL MRS Global detectors BB : Provide vertex and start time for TOF (and forward multiplicity) MA : Provide multiplicity / centrality of collision Silicon Strips

Plastic Scintillator Tiles Multiplicity at s 200 from MA and BB NN BRAHMS Preliminary 0-5% 5-10% 10-20% 20-30% 30-40% 40-50% 4630 370 charged particles

produced for 0-5 % central. 21 % increase over 130 GeV dNch/d (=0) = 625 55(syst.) 14% increase over 130 GeV. Phobos 200 GeV : PRL 88, 22302 : dNch/d (=0) = 650 35(syst.) 200 GeV : Submitted to PRL (nucl-ex/0112001) 130 GeV : Phys. Lett. B 523, p. 227 Comparison to scaled p p and models BRAHMS Preliminary pp

p p data(UA5, Z. Phys. C 33, 1) : BRAHMS data shows 50% increase at = 0 Models : Kharzeev and Levin (solid) and AMPT(dashed) describes the data well. dN/d vs. BRAHMS Preliminary Charged Particle Mult. snn=130GeV SPS BRAHMS. Phys Lett. B. 523 227 (2001)

Limiting fragmentation: SPS=>RHIC 200 GeV top 5% 130 GeV top 5% 200 GeV 30-40% SPS Pb- Pb(NA49) dN/d vs Npart Kharzeev and Levin (nucl-th/0108006) Soft-Hard:

dN/d=(1-X) n) npp /2 + X) n npp =1049, =339, npp=2.43 =>dN/d=668 (with X) n=0.9) High Density QCD-saturation: dN/dy =f(Npart,Qs2,,QCD,s,y) with =0.3 from HERA data => dN/d=620 Fit to dNch /d = ANpart+ BNcoll: (using dN/d=549ats=130GeV) 130: A= 1.24 0.080.2, B =0.12-+0.04-+0.06 200: A= 1.26 0.090.2 B =0.15-+0.04-+0.05

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) AMPT dashed line top 5% 30-40 K&L solid line 5-10 40-50 Ratios of particles and anti-particles at

sNN 200 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 s 200 .

NN N ( K p ) N (K ) N ( K ) N ( K p ) N ( K ap ) BRAHMS Preliminary ( p p p K ) N( pp)

N ( p) N ( p ) N ( p p ) N ( pt ) (and feeddown) PRL 87, 2001 Ratios vs Pt and centrality BRAHMS Preliminary BRAHMS Preliminary No sign of Pt or centrality dependence

Pbar/p increases slowly with S We dont yet understand baryon transport AMPT S dependence, towards matter/antimatter balance Preliminary Protons Kaons Estimate of net protons at midrapidity CM Energy

N(p) sNN 17 GeV 31 5 26* sNN 130 GeV 29

20 9* sNN 200 GeV (30) (23) (7)* N(p)

N(p) - N(p) N ( p pair ) * NA49 QM99 & Phys. Rev. Lett. 82, 2471 (1999) N ( p) N ( p ) N ( p pair ) N ( pother ) * PHENIX) n nucl-ex/0112006 * Assuming 14% more pbar (cf. dN/d, BRAHMS sub to PRL dec.2001) and N ( p ) / N ( p ) 0.75. Summary First Au+Ausnn=130 ,200 GeV

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

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

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