Brahms: Forward Physics at RHIC

1. T2 FS: 6 deg 0.8 msr T1 Dipole Magnets MRS: 90 deg 6.5 msr MTPC1 MTPC2 Brahms: Forward Physics at RHIC Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

2. 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 Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

3. FOWARD 1<h<3.6 GLOBAL MRS -0.5<h<1 Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

4. Silicon Strips Plastic Scintillator Tiles Global detectors BB : Provide vertex and start time for TOF (and forward multiplicity) MA : Provide multiplicity / centrality of collision Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

5. Multiplicity at from MA and BB BRAHMS Preliminary 0-5% 5-10% 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 10-20% 20-30% 30-40% 40-50% Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

6. BRAHMS Preliminary 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. pp Comparison to scaled and models Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

7. dN/dh vs. h BRAHMS Preliminary Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

8. SPS Charged Particle Mult.snn=130GeV BRAHMS. Phys Lett. B. 523 227 (2001) Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

9. 200 GeV top 5% 130 GeV top 5% 200 GeV 30-40% SPS Pb- Pb(NA49) Limiting fragmentation: SPS=>RHIC Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

10. Fit to dN /dh = AN + BN : ch part coll • 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) dN/dh vs Npart 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 Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

11. 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. Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

12. dN(200GeV)/dN(130GeV) AMPT dashed line K&L solid line 5-10 top 5% 30-40 40-50 Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

13. 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. Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

14. 2 Ring Imaging Cherenkov Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

15. ▄ PRL 87, 2001 Rapidity dependence of ratios at . BRAHMS Preliminary (and feeddown) Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

16. Ratios vs Pt and centrality BRAHMS Preliminary BRAHMS Preliminary No sign of Pt or centrality dependence Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

17. Pbar/p increases slowly with √S Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

18. We don’t yet understand baryon transport AMPT Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

19. √S dependence, towards matter/antimatter balance Preliminary Protons Kaons Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

20. CM Energy N(p) 26* 31 5 17 GeV 9* 20 130 GeV 29 (7)* (30) (23) 200 GeV * NA49 QM99 & Phys. Rev. Lett. 82, 2471 (1999) * PHENIX nucl-ex/0112006 * Assuming 14% more pbar (cf. dN/dη, BRAHMS sub to PRL dec.2001) and 0.75. Estimate of net protons at midrapidity Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT

21. 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 Summary First Au+Ausnn=130 ,200 GeV Michael Murray, Texas A&M, CMS Heavy Ion Mtg at MIT