1. Recent Results from PHOBOS David Hofman – UIC For the Collaboration AGS/RHIC Users Meeting May 15-16, 2003, BNL

2. AGS/RHIC Users Meeting 20032 Collaboration (May 2003) 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 Pradeep Sarin

3. AGS/RHIC Users Meeting 20033 The PHOBOS Detector in 2002 137000 Silicon Pad Channels 1m Nearly 4  Coverage   0+3-3 +5.4 -5.4 Octagon Ring Counters Spectrometer ZDC Triggering ZDC

4. AGS/RHIC Users Meeting 20034 PHOBOS Data on dN/d  in 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.

5. AGS/RHIC Users Meeting 20035 Au+Au  Surprising: ratio of hard/soft collisions is the same. Charged Particle Production at Midrapidity Energy and Centrality Dependence 19.6 GeV preliminary 130 GeV 200 GeV Midrapidity |  |<1  Published at 130 and 200 GeV: PRC 65, 061901(R) (2002); 19.6 GeV in Preparation dN ch /d  two component fit with x~ 0.1 pp 19.6 GeV preliminary 130 GeV 200 GeV Data is normalized by corresponding pp value for each energy. pp

6. AGS/RHIC Users Meeting 20036 Charged Particle Production (dN/d  ) 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 p + p inel. UA5, Z.Phys.C33, 1 (1986) dN/d   Growth of the Fragmentation Region with  s NN  Status: In Print for PRL

7. AGS/RHIC Users Meeting 20037 Centrality dependence of  N ch  Error bands due to high-  extrapolation (preliminary)  Total charged particle production ~ N part and consistent with e + e - Au+Au

8. AGS/RHIC Users Meeting 20038 Comparison vs. Energy  Surprising agreement at high energy  nucl-ex/0301017; Submitted for Publication

9. AGS/RHIC Users Meeting 20039 Preliminary v 2 200 Final v 2 130 PHOBOS Au-Au v2v2  200 130 ~190 Elliptic Flow (v 2 ) at 130 and 200 GeV PRL 89, 222301  PRELIMINARY 200 GeV results very similar to 130 GeV  130 GeV Data Published in PRL 89, 222301 (2002)  See Poster by Carla Vale for 200 GeV Track-based Results

10. AGS/RHIC Users Meeting 200310 Systematic Errors not shown Phobos Preliminary P T Distribution of Charged Particles  Phobos has capabilities to measure from p T, = 0.030 – 5 GeV/c

11. AGS/RHIC Users Meeting 200311 Invariant yields of very low p T particles (++)(++) (K + +K – ) (p+p) PHOBOS preliminary p T [GeV/c] 1/ (2  p T )d 2 N/dydp T X[cm ] A B C D E F Z[cm] Beam pipe 0 10 20 Z [cm] 0 10 20 → Mass measurement by ‘energy- range’ method in 5 planes of silicon.  Unique: Can measure down to very low p T.  Status of Experimental Result: In Preparation for Publication p T = 0.03 – 0.20 GeV/c

12. AGS/RHIC Users Meeting 200312 Interest in RHIC data is extremely high; Preliminary Data already ‘Published’ P. Kolb and R. Rapp; PRC 67 044903

13. AGS/RHIC Users Meeting 200313 Particle Ratios: Energy dependence p/p K – /K + p T = 0.07 – 1.0 GeV/c  PHOBOS 130 GeV PRL 87,102301,2001 (  B ~45 MeV)  PHOBOS 200 GeV (  B ~27 MeV)  Rapidly decreasing net baryon density near midrapidity  200 GeV Result is published: PRC 67, 021901(R) (2003) A+A central collisions

14. AGS/RHIC Users Meeting 200314  At 200 GeV, minimum bias pp reference data exist for comparison. Transverse Momentum Distributions for Au+Au @ 200 GeV 0.2<y   <1.4

15. AGS/RHIC Users Meeting 200315 Comparing Au+Au spectra to pp  Excess yield at 2 GeV/c  BUT, at higher energy the particle yields appear to come back ‘down’ to the pp value.

16. AGS/RHIC Users Meeting 200316 Ratio of Au+Au and pp spectra at 200 GeV We observe a significant change in the spectral shape between pp and Au+Au collisions. Central Au+Au collisions show an approximate scaling with the number of participants for low and high p T. mid-peripheral central N part = 65 ± 4 N part = 344 ± 12

17. AGS/RHIC Users Meeting 200317 Evolution with Centrality (Au+Au) Divide spectra by fit to mid- peripheral 45-50% centrality bin. Gradual change of shape. Peak develops at 1.5 GeV/c. Low and high p T ‘matches’ the mid-peripheral yields. mid-peripheral central Yield/ / mid-peripheral fit

18. AGS/RHIC Users Meeting 200318 Centrality scaling in p T bins (Au+Au) Spectra normalized to a fit at mid-peripheral 45-50% bin.  Over the centrality range studied, for low and high p T, the Au+Au data scale approximately with number of participants.  nucl-ex/0302015; Submitted for Publication

19. AGS/RHIC Users Meeting 200319 This Year: PHOBOS Detector 2003  Moved TOF walls back ~ 5 m from interaction point  Installed new spectrometer trigger detector that selects on high p T tracks  Installed new “time-zero” (T0) Cerenkov detectors to provide triggering and on-line vertexing as well as a start time for our TOF walls.  Proton calorimeter on Gold and Deuteron “going” sides for dA run SPECTRIG T0 mini-pCal pCal  x15 high p T data  See Poster By C. Henderson, J. Kane and G. Veres pCal Sum Energy (a.u.)  See Posters by A. Iordanova and R. Hollis

20. AGS/RHIC Users Meeting 200320 PHOBOS Preliminary Results from d+Au Four centrality bins based on energy in our Silicon Ring detectors 0.2<  <1.4 Centrality Determination: Energy in Silicon Ring Counters Energy (arb. units ) Counts 3.0<|  |<5.4 Transverse Momentum Distributions in d+Au PHOBOS d+Au preliminary 0 – 20% 20 – 40% 40 – 70% 70 – 100%

21. AGS/RHIC Users Meeting 200321 PHOBOS Preliminary Results from d+Au PHOBOS preliminary PHOBOS preliminary PHOBOS preliminary PHOBOS preliminary R dAu Yield/ /p+p fit peripheral central

22. AGS/RHIC Users Meeting 200322 Summary and Outlook 5 papers (3 published and 2 submitted) since last AGS/RHIC Users’ Meeting. 5 additional papers from Au+Au data are in progress. First look at new results for d+Au shows qualitatively different features as compared to Au+Au! Exciting times at RHIC and PHOBOS. Many thanks to the entire RHIC crew for supplying us the beams.

23. AGS/RHIC Users Meeting 200323 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