1. Robert Pak (BNL) for the PHOBOS Collaboration Quark Matter 2001 Jan. 16, 2001 The PHOBOS Detector at RHIC Present Status and Future Plans

2. Robert Pak for PHOBOS Collaboration ARGONNE NATIONAL LABORATORY Birger Back, Nigel George, Alan Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Mathew Ceglia, Alan Carroll, Stephen Gushue, George Heintzelman, Hobie Kraner, Robert Pak, Louis Remsberg, Joseph Scaduto, Peter Steinberg, Andrei Sukhanov INSTITUTE OF NUCLEAR PHYSICS, KRAKOW Wojciech Bogucki, Andrzej Budzanowski, Tomir Coghen, Bojdan Dabrowski, Marian Despet, Kazimierz Galuszka, Jan Godlewski, Jerzy Halik, Roman Holynski, W. Kita, Jerzy Kotula, Marian Lemler, Jozef Ligocki, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki, Andrzej Straczek, Marek Stodulski, Mieczylsaw Strek, Z. Stopa, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak, Pawel Zychowski JAGELLONIAN UNIVERSITY, KRAKOW Andrzej Bialas, Wieslaw Czyz, Kacper Zalewski MASSACHUSETTS INSTITUTE OF TECHNOLOGY Wit Busza*, Patrick Decowski, Piotr Fita, J. Fitch, C. Gomes, Kristjan Gulbrandsen, P. Haridas, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Clyde Law, Johannes Muelmenstaedt, Marjory Neal, P. Patel, Heinz Pernegger, Miro Plesko, Corey Reed, Christof Roland, Gunther Roland, Dale Ross, Leslie Rosenberg, John Ryan, Pradeep Sarin, Stephen Steadman, George Stephans, Katarzyna Surowiecka, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch NATIONAL CENTRAL UNIVERSITY, TAIWAN Yuan-Hann Chang, Augustine Chen, Willis Lin, Jaw Luen Tang UNIVERSITY OF ROCHESTER Adam Hayes, Erik Johnson, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs UNIVERSITY OF ILLINOIS AT CHICAGO Russell Betts, Christopher Conner, Clive Halliwell, Rudi Ganz, Richard Hollis, Burt Holzman, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter UNIVERSITY OF MARYLAND Richard Baum, Richard Bindel, Jing Shea, Edmundo Garcia-Solis, Alice Mignerey

3. Robert Pak for Primary Physics Objectives PHOBOS searches for signatures of QGP at RHIC » Multiplicity of charged particles for |  | < 5.4 » Particles down to low p T near y = 0 » Particle ratios, spectra, and correlations PHOBOS “lives” on analog signals of our silicon detectors » dE/dx as multiplicity estimator » dE/dx method for particle identification » Background rejection » Pattern recognition

4. Robert Pak for PHOBOS Apparatus Cerenekov Trigger CountersTime of Flight Counters Octagon Multiplicity Detector + Vertex Detector (Silicon) Spectrometer Detectors (Silicon) Beryllium Beam Pipe Paddle Trigger Counters Magnet (top part removed) Ring Multiplicity Detectors (Silicon)

5. Robert Pak for  t (ns) Events Event Selection Negative Paddles Positive Paddles ZDC NZDC P Au x z PP PN Paddle Counters Coincidence (38 ns) between paddle counters

6. Robert Pak for 3<|  |<4.5  Centrality with Paddles Negative Paddles Positive Paddles ZDC NZDC P Au x z PP PN Energy deposited in paddle counters e.g., top 6% most central collisions Events/Bin Entries

7. Robert Pak for Centrality with ZDCs peripheral central See J.M. Katzy in Parallel Session II for details ZDC sum vs. Paddle sum: Independent methods to determine centrality that correlate well ZDC Paddle Sum (au) ZDC Sum (au)

8. Robert Pak for Double Metal, single-sided, AC coupled, polysilicon biased detectors produced by ERSO in Taiwan AC coupled pad (p-implant + metal 1 pad) polysilicon bias resistor metal 2 readout line contact hole metal 1- metal 2 Silicon Pad Technology p+ implant n+ polysilicon drain resistor bias bus signal lines vias  m 5k  nSi 0.  m ONO 1.  m ONO +HV

9. Robert Pak for Silicon Pad Sensors High dynamic range ( > 100 MIPs), peaking time 1.1  s Si latch-up system interlocks during single-event upset to protect against chip damage Typical pad layout 14 cm IDE VA-HDR1 Readout Chips

10. Robert Pak for Octagon/Vertex Spectrometer Arm Silicon Everywhere Ring 137,000 channels in total

11. Robert Pak for Si Signal Simulation Vertex signal response Full understanding of detector signal at the most basic level angle corrected @ 300  m of Si normalized hit energy x 0 dE dx [keV]

12. Robert Pak for Sensor Uniformity +/- 1% +/- 3% No substantial signal variation due to different layout (double metal line routing and/or varying pad size) 8.5 cm 6.5 cm signal (keV) S mp = 93 keV S mp = 85 keV counts signal (keV) Rings Octagon

13. Robert Pak for Signal/Noise Ratios S/N ratios better than 10:1 design specification Larger pads & longer readouts lower S/N ratio Ave. noise in entire detector setup stable over time no. of days

14. Robert Pak for  E (“MIP”) 2 0 6 4 -2 -6 -4 0 4 8 12 2 0 6 4 -2 -6 -4  E (“MIP”) 0 4 8 12 Data Monte Carlo   Background Suppression  E vs.  in the Octagon Good agreement between data and simulation Powerful method to reject background Si from vertex not from vertex

15. Robert Pak for Multiplicity & Vertex Array Vertex Octagon Ring Multiplicity:Vertex: Single layer of Si with large pads Two layers of Si with “strip” pads Count single hits or sum of analog signals in a detector area as a measure of particle multiplicity

16. Robert Pak for Vertex Determination cm Vertex Resolution:  x ~ 450  m  y ~  z ~ 200  m For this event: vertex @ Z = -0.054 cm cm counts +z Si

17. Robert Pak for Multiplicity Array Unrolled 0 +3-3+5.4-5.4 Spec   Rings Vertex Octagon

18. Robert Pak for See A.H. Wuosmaa in Monday Plenary Session for details Also Collective Effects: See I.C. Park in Parallel Session II  Octagon3 Rings Run 5374 Event 79495 entries Multiplicity Distribution

19. Robert Pak for PHOBOS Magnet B Field Map B y (T) cm Reproducibility of absolute field strength better than 1%

20. Robert Pak for Particle ID with the spectrometer See N.K. George in Parallel Session III for details  p K Full Tracking protons Kaons pions

21. Robert Pak for Run 5332 Event 35225 08/31/00 06:59:24 PHOBOS Online Event Display Spectrometer Arm N Spectrometer Arm P Octagon Multiplicity detector Trigger Scintillators N Trigger Scintillators P Not to scaleNot all sub-detectors shown Au-Au Beam Momentum = 65.12 GeV/c

22. Robert Pak for PC VME RACE way Data from silicon detectors 2*50 MB/sec VME RACEway crossbar switch Processing boards UltraSparc Gigabit Ethernet 5MB/sec 80 MB/sec 140 MB/sec each 40 MB/sec Run 2000: Data taking rate: 15 ev/sec Sustained: 5 MB/sec 8 PowerPC’s Run 2001: Goal: 100 ev/sec Sustained: 40 MB/sec New features: Direct VME  Gigabit Multi-buffering Compression 2:1 22 PowerPC’s PHOBOS DAQ

23. Robert Pak for Summary of 2000 Run RHIC delivered ~ 2.7  b -1 integrated luminosity to PHOBOS over 6 weeks of running in Summer 2000. PHOBOS captured ~ 3.5M events on tape: mixture of minimum bias and central triggers; 99% DAQ uptime. Silicon systems performed to specifications: Average S/N measured in the detector was 14 to 18 depending on sensor type; 98% channels fully functional. Front End Electronics were stable. Every instance of latch-up in the VA chips was detected successfully during adverse beam conditions.

24. Robert Pak for Future Plans: 2001 Run DAQ upgrade Complete installation of 2 nd spectrometer arm » Significantly improved 2-particle phase space  HBT for small sources      down to p T = 0  Back-to-back high p T particles » Doubles the one-particle statistics » Symmetric system improves systematics

25. Robert Pak for PHOBOS Charm Upgrade Open charm measurement is essential for understanding total charm production D e _ + X is best suited for small acceptance near midrapidity Study single electrons at high p T from displaced vertices Suppress the hadronic background Upgrade PHOBOS with: » microvertex detector » ALICE Transition Radiation Detector prototypes » Electromagnetic calorimeter TRD EMCal  vertex

26. Robert Pak for Stay tuned to: www.phobos.bnl.gov Drop by PHOBOS IR during your BNL Day Tour today ConclusionConclusion Robert Pak for