1. EPS Meeting AachenGerrit van Nieuwenhuizen Charged Particle Production in Au+Au at RHIC Gerrit van Nieuwenhuizen Massachusetts Institute of Technology For the Collaboration

2. EPS Meeting AachenGerrit van Nieuwenhuizen The PHOBOS Detector 137000 Silicon Pad Channels 1m Nearly 4  Coverage   0+3-3 +5.4 -5.4 Octagon Ring Counters Spectrometer ZDC Triggering ZDC

3. EPS Meeting AachenGerrit van Nieuwenhuizen dN/d  for Au+Au vs. Centrality and  s dN/d    19.6 GeV130 GeV 200 GeV PHOBOS Typical systematic band (90%C.L.)  Extensive systematic multiplicity data set.

4. EPS Meeting AachenGerrit van Nieuwenhuizen In the beginning: dN/d  at  Tracklets Quick & Dirty for every new collision energy

5. EPS Meeting AachenGerrit van Nieuwenhuizen Energy Dependence of Central Yields at  =0 A + A For central 6% collisions at midrapidity for RHIC full energy

6. EPS Meeting AachenGerrit van Nieuwenhuizen Au+Au  Fraction of ‘hard’ (10%) to ‘soft (90%) is about the same for all energies. Charged Particle Production at Midrapidity Energy and Centrality Dependence 19.6 GeV preliminary 130 GeV 200 GeV Midrapidity |  |<1 dN ch /d  two component fit with x~ 0.1 pp PRC 65, 061901(R) (2002); 19.6 GeV in Preparation

7. EPS Meeting AachenGerrit van Nieuwenhuizen  Ratio of hard/soft collisions is the same for all energies Charged Particle Production at Midrapidity Midrapidity |  |<1 dN ch /d  19.6 GeV preliminary 130 GeV 200 GeV Data is normalized by corresponding pp value for each energy. pp Au+Au Energy and Centrality Dependence

8. EPS Meeting AachenGerrit van Nieuwenhuizen Centrality Dependence of Total  N ch  Error bands due to high-  extrapolation  Total scales with N part and is consistent with e + e - Au+Au # of charged particles (central collision): 5060±250 @ 200 GeV 4170±210 @ 130 GeV 1680±100 @ 19.6 GeV (preliminary)

9. EPS Meeting AachenGerrit van Nieuwenhuizen e + e - measures dN/dy T (rapidity relative to “thrust” axis) 200 GeV  Au + Au and e + e - similar in shape as well as magnitude. dN/d  Shape Au + Au and e + e -

10. EPS Meeting AachenGerrit van Nieuwenhuizen The “Leading Proton” Effect ss  s eff Basile et al (1980-1984) pQCD e + e - Calculation (A. Mueller, 1983)

11. EPS Meeting AachenGerrit van Nieuwenhuizen Total  N ch  vs. Energy: Heavy Ion data pQCD e + e - Calculation nucl-ex/0301017  Surprising agreement at high energy

12. EPS Meeting AachenGerrit van Nieuwenhuizen Reaction plane x z y x y z Collectivity: Elliptic Flow dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R )) +... ) Elliptic flow Initial state spatial anisotropy mapped onto the final state particle production. Azimuthal distribution of charged particles

13. EPS Meeting AachenGerrit van Nieuwenhuizen v2 vs N and  v2v2 200 130 ~190 PRL 89, 222301  part  Not Boost Invariant !  Reaches Hydro-Limit for most central  Reaches Hydro-Limit for 

14. EPS Meeting AachenGerrit van Nieuwenhuizen Flow: Track-based Vertex measurement Reaction plane determined by hits in widely separated subevent regions, symmetric in ,  Correlate tracks in spectrometer to reaction plane to determine v 2

15. EPS Meeting AachenGerrit van Nieuwenhuizen PHOBOS preliminary PHOBOS preliminary PHOBOS preliminary PHOBOS preliminary R dAu PHOBOS preliminary h + + h - 200 GeV Au+Au 0<  <1.5 (top 55%) v 2 17% scale error v2 vs Transverse Momentum  v2 ‘saturates’ above 2 GeV/c  Similar Pt behavior as for nuclear modification factor See Rachid Nouicer’s talk d+Au

16. EPS Meeting AachenGerrit van Nieuwenhuizen Collaboration Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts, Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan Carroll, Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Stephen Gushue, Clive Halliwell, Joshua Hamblen, Adam Harrington, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Erik Johnson, Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Jang Woo Lee, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Aaron Noell, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Christof Roland, Gunther Roland, Joe Sagerer, Pradeep Sarin, Pawel Sawicki, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Ray Teng, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Bernard Wadsworth, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch, Jinlong Zhang ARGONNE NATIONAL LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER

17. EPS Meeting AachenGerrit van Nieuwenhuizen Centrality (Npart) in Au+Au Data Paddle signal Data+MC HIJING +GEANT Glauber calculation Model of paddle trigger Peripheral b Central b N part Paddle: Multiplicity in 3 < |  | < 4.5 Paddles ZDC Au Paddles Monotonic relation Paddles and ZDC’s

18. EPS Meeting AachenGerrit van Nieuwenhuizen The Fragmentation Region in Au + Au Scale by /2 & shift to  =  - y beam PHOBOS Au+Au dN ch /d  Systematic errors not shown PHOBOS Au+Au dN ch /d  / /2 6% central  ‘Universal’ Fragmentation Region at Rest Frame of one Ion. Phys. Rev. Lett. (2003), in press

19. EPS Meeting AachenGerrit van Nieuwenhuizen Au + Au Fragmentation Region and p + p Systematic errors not shown PHOBOS Au+Au dN ch /d  / /2 6% central p + p inel. UA5, Z.Phys.C33, 1 (1986) dN/d   Growth of the Au + Au Fragmentation Region with  s NN similar as in p + p

20. EPS Meeting AachenGerrit van Nieuwenhuizen   RingsN Octagon RingsP Reaction plane determined by subevents in -2<  <2 Elliptic flow (v 2 ) determined for |  |<5.3 Select vertices offset in Z, symmetric coverage in ,  Flow: Hit-based method

21. EPS Meeting AachenGerrit van Nieuwenhuizen Comparison of Total  N ch  vs. Energy Different systems converge at high energy. PHOBOS Preliminary Central Au+Au Central AA pp (pp) data @  s eff e+e-e+e- 1 10 10 2 10 3  s (GeV) nucl-ex/0301017