1. VERTEX2003, Low Hall, Cumbria The PHOBOS Detector “Design, Experience and Analysis” RUSSELL BETTS for The PHOBOS Collaboration

2. VERTEX2003, Low Hall, Cumbria 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 Holynski, 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 Wozniak, Alan Wuosmaa, Bolek Wyslouch, 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

3. VERTEX2003, Low Hall, Cumbria The PHOBOS Detector (2001) 137000 Silicon Pad Channels 1m 12m Be Beampipe Spectrometer Octagon Vertex Ring Counters Paddle Trigger Counter Cerenkov Counter DX magnetDX Magnet ZDC

4. VERTEX2003, Low Hall, Cumbria Bias Bus p+ Implant n+ Polysilicon Drain Resistor Signal Lines vias 300µm 5k  nSi 0.2um ONO 1.2um ONO Double Metal, Single Sided, AC Coupled, Polysilicon Biased Produced by ERSO, Taiwan Conservative Design, but 9 Types Common Readout with IDEAS VA HDR 64/128 Channel Chip Silicon Sensors

5. VERTEX2003, Low Hall, Cumbria Silicon Detector Modules Used in the Octagon Module 8.5cm 6.5 cm 120 pads / sensor  ~0.05 - 0.1  =  /16 64 pads / sensor  ~0.05  =  /32 Ring Module Multiplicity Array

6. VERTEX2003, Low Hall, Cumbria Assembled Elements of the Multiplicity Array Partially assembled Octagon Ring arrays Inner Vertex Outer Vertex

7. VERTEX2003, Low Hall, Cumbria Ring Counter Octagon Detector Vertex Detector Octagon and Vertex Prior to Insertion in Magnet Gap Ring Counter around 1mm Be Beampipe

8. VERTEX2003, Low Hall, Cumbria Spectrometer Modules

9. VERTEX2003, Low Hall, Cumbria Spectrometer Arm 18 sensors x 500 ch. 28 sensors x 512 ch. 66 sensors x 256 ch 21 sensors x 256 ch. 8 sensors x 1536 ch.

10. VERTEX2003, Low Hall, Cumbria Signal/Noise Distribution Source Test : Ring Detector pad pulse height Counts Peak S/N = 16 Acceptance criteria for Module : - bad channels < 5 % - S/N > 10

11. VERTEX2003, Low Hall, Cumbria Running Experience at RHIC Summer 2000 - Commissioning and First Collisions at sqrt(s) = 56 and 130 GeV/u Au+Au. Detector 98% Functioning. Summer 2001 - January 2002 – Long Au+Au run at 200 GeV/u. First pp data. 24 hr run at 19.6 GeV/u November 2002 – May 2003 – d+Au and pp at 200 GeV/u Au+Au d+Au 130 GeV/u 200 GeV/u

12. VERTEX2003, Low Hall, Cumbria Radiation Monitoring with Real Time Detectors and TLDs

13. VERTEX2003, Low Hall, Cumbria Radiation Exposure Chronic Radiation Dose not Troublesome – kRad. Acute Incidents a Significant Problem High Levels During Beam Tuning – Detector Turned Off “Blast” Events Due to Beam Misadventures with Detector On – Abort Kicker Malfunction. Damage to Readout Chips – Particularly Calibration Circuits. Partially Recovered by Adjustment of Control Voltages.

14. VERTEX2003, Low Hall, Cumbria Dead Channels after Beam Blast RingN RingP Octagon Just after the beam blasted the detector After readjusting the VA chip operating parameters

15. VERTEX2003, Low Hall, Cumbria  +5.4 0+3-3-5.4 Multiplicity Measurement Hit Counting in Octagon and Rings plus Poisson Correction for High Occupancy. Energy Deposition to count MIPs. “Tracklets” in Vertex and Spectrometer OctagonRings

16. VERTEX2003, Low Hall, Cumbria PHOBOS Data on dN/d  dN/d    19.6 GeV130 GeV 200 GeV Preliminary Extensive and Systematic Data Set PHOBOS Typical systematic error band (90%C.L.)

17. VERTEX2003, Low Hall, Cumbria Energy Dependence of Central dN/d  Scale by N part /2 & Shift to  =  - y beam The “Fragmentation Region” grows with  s NN 19.6 GeV is preliminary19.6 GeV is preliminary Systematic errors not shown PHOBOS Au+Au dN ch /d  / dN ch /d  6% central

18. VERTEX2003, Low Hall, Cumbria Flow - v 2 vs  and  s Averaged over Centrality PHOBOS Au+Au Preliminary v 2 200 Final v 2 130 200 GeV 130 GeV nucl-ex/0205021

19. VERTEX2003, Low Hall, Cumbria Total Multiplicity for AA and pp (pp) 19.6 GeV is preliminary AA data is central

20. VERTEX2003, Low Hall, Cumbria Remove the “Leading Proton” Effect ss  s eff Basile et al (1980-1984) pQCD e + e - Calculation (A. Mueller, 1983)

21. VERTEX2003, Low Hall, Cumbria Comparison of  N ch  vs. Energy pQCD e + e - Calculation

22. VERTEX2003, Low Hall, Cumbria Comparison of  N ch  vs. Energy Different Systems Converge at High Energy. Universality of N ch ? PHOBOS Preliminary Central Au+Au Central AA pp (pp) data @  s eff e+e-e+e- 1 10 10 2 10 3  s (GeV)

23. VERTEX2003, Low Hall, Cumbria  N ch  scales with N part Error bands due to high-  extrapolation Au+Au (preliminary) Total Charged Particle Production ~ N part

24. VERTEX2003, Low Hall, Cumbria Summary PHOBOS Silicon has Proved Robust and Stable. Successfully Operated Through Three Runs and Largely Survived Several Incidents. Physics Results from Multiplicity Display Interesting Scaling Behavior. PHOBOS Spectrometer Results (not shown) Add New Information on Observed Phenomenon of Suppression of High p T Particles.