1. H. Ito University of Kansas For the BRAHMS Collaboration The BRAHMS Institutions 1 Brookhaven National Laboratory, Upton, NY 11973, U.S.A. 2 Institut de Recherches Subatomiques and Université Louis Pasteur, Strasbourg, France 3 Institute of Nuclear Physics, Krakow, POLAND 4 Jagellonian University, Krakow, POLAND 5 Johns Hopkins University, Baltimore, MD 21218, U.S.A. 6 New York University, New York, NY 10003, U.S.A. 7 Niels Bohr Institute for Astronomy, Physics and GeophysicsUniversity of Copenhagen, Copenhagen Ø, DENMARK 8 Texas A&M University, College Station, TX 77843-3366, U.S.A. 9 Fysisk institutt, Universitetet i Bergen, Bergen, NORWAY 10 University of Bucharest, ROMANIA 11 University of Kansas, Lawrence, KS 66045, U.S.A. 12 University of Oslo, Oslo, NORWAY + Deceased Charged Particle Multiplicities at BRAHMS 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 3, R. Debbe 1, J. J. Gaardhøje 7, K. Grotowski 4, K. Hagel 8, O. Hansen 7, A. Holm 7, A. K. Holme 12, H. Ito 11, E. Jakobsen 7, A. Jipa 10, J. I. Jørdre 9, F. Jundt 2, C. E. Jørgensen 7, T. Keutgen 8, E. J. Kim 5, T. Kozik 4, T. M. Larsen 12, J. H. Lee 1, Y. K. Lee 5, G. Løvhøiden 12, Z. Majka 4, A. Makeev 8, B. McBreen 1, M. Murray 8, J. Natowitz 8, B. S. Nielsen 7, K. Olchanski 1, J. Olness 1, D. Ouerdane 7, R. Płaneta 4, F. Rami 2, D. Röhrich 9+, B. H. Samset 12, S. J. Sanders 11, R. A. Sheetz 1, Z. Sosin 4, P. Staszel 7, T. F. Thorsteinsen 9, T. S. Tveter 12, F. Videbæk 1, R. Wada 8, A. Wieloch 4 and I. S. Zgura 10

2. Perspective View of BRAHMS Detectors

3. Perspective View of Global Detectors

4. Beam Beam Counter 2 Size of Cherenkov Radiators 3/4 in  x 3 cm and 2 in  x 4 cm Coverage 2.5 < |  | < 4.7 Located 219 cm from the vertex Left Array Right Array

5. Multiplicity Array Two Layers: 175 Silicon-detector channels.86 cm x 4 cm x.3 mm 38 Scintillator tiles 12 cm x 12 cm x.5 cm coverage -2.2 <  < 2.2

6. Multiplicity By Beam Beam Counter from Detected Energy

7. Multiplicity By Beam Beam Counter from Statistics Assumptions Poisson probability distribution Good measurement of no hit

8. Beam Beam Counter Background Correction

9. Multiplicity Array Energy Calibration Using 1 MIP response from data, the detected energy is calibrated for each detector. Solid line: experimental data Dotted line: GEANT simulation

10. Multiplicity By Multiplicity Array From the Detected Energy to N Model dependence is a few percent (HIJING and FRITIOF) There is no centrality dependence. Using GEANT Monte Carlo Simulation, get N ch /E MIP for each detector element   Beam Axis GEANT

11. Centrality Determination Two Methods of Measuring Centrality Centrality by Multiplicity Array Centrality by ZDC and BB Preliminary Results

12. dN/d  Preliminary Results 0-5%5-10% 10-20%20-30% 30-40%40-50% Beam Beam Counter Silicon Tile T1 TPM1

13. dN/d  with model prediction Preliminary Results Fritiof Hijing

14. dN/d  per Participant Pair Preliminary Results FRITIOF HIJING EKRT Eikonal (Kharzeev and Nardi) Npart from Glauber Model Npart from Eikonal Model PHENIX

15. Conclusion Charged particle multiplicities have been measured over a wide range of . Pseudorapidity distributions have been measured with different centralities. dN/d  per participant pair has been measured with different centralities and pseudorapidities. However, the uncertainty in for peripheral collision seems to be too large to detemine a definitive trend.