1. Gerrit J. van Nieuwenhuizen For the PHOBOS collaboration Experience & Upgrade RHIC future detectors R&D Workshop Brookhaven National Laboratory November 13-14, 2001

2. The PHOBOS collaboration " ARGONNE NATIONAL LABORATORY " BROOKHAVEN NATIONAL LABORATORY " INSTITUTE OF NUCLEAR PHYSICS, KRAKOW " MASSACHUSETTS INSTITUTE OF TECHNOLOGY " NATIONAL CENTRAL UNIVERSITY, TAIWAN " UNIVERSITY OF ROCHESTER " UNIVERSITY OF ILLINOIS AT CHICAGO " UNIVERSITY OF MARYLAND " Birger Back, Nigel George, Alan Wuosmaa " Mark Baker, Donald Barton, Alan Carroll, Joel Corbo, Stephen Gushue, Dale Hicks, Burt Holzman, " Robert Pak, Marc Rafelski, Louis Remsberg, " Peter Steinberg, Andrei Sukhanov " Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak " Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Michel Rbeiz, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch " Chia Ming Kuo, Willis Lin, Jaw-Luen Tang " Joshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs " Russell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer " Richard Bindel, Alice Mignerey

3. And the Experiments 2000: Au+Au @  s= 56 AGeV Au+Au @  s= 130 AGeV Au+Au @  s= 130 AGeV 2001: Au+Au @  s= 200 AGeV 2002-200x: Take Data 2001

4. PHOBOS Detector Overview

5.  Measuring charged particle multiplicity with Octagon/Rings  Determining the interaction point with Vertex Detector  Do 3d-tracking with Spectrometer Arms  Use dE/dx for particle identification Silicon Sensor Tasks

6. AC coupled Pad (p-implant + metal 1 pad) polisilicon 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 300um 5kOhm nSi 0.2um ONO 1.2um ONO Double Metal, Single sided, AC coupled, polysilicon biased detectors produced by ERSO, Taiwan Conservative design, but 9 types

7. Detector modules

8. Spectrometer 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.

9. Multiplicity detector Octagon & Vertex Ring counter * 6

10. PHOBOS Readout scheme Silicon Detector Modules Front End Controllers Silicon Pad detectors ~1500 pads IDE VA and VA - HDR1 Readout Chips ANALOG Data Multiplexer Unit Mercury RACEway/VME Zero Suppression System DIGITAL G-LINK FIBRE- OPTIC Event Builder DISKS 100Mbps UDP Trigger Detectors TOF array LeCroy FASTBUS ADC + TDC modules VME+NIM based Trigger Management 100Mbps UDP ANALOG L0, L1 TRIGGE R Not zero supressed to study details of detector response

11. Events in 2001 and 2000

12. First RHIC Results in 2000 and 2001 Charged Particle Multiplicity at MidRapidity 3 weeks after first 2000 collisions 10 days after first 2001 collisions PRL 85 3100 (2000) nucl-ex/0108009 PRL in press

13. Signal Response & Stability

14. Baseline Corrections • High Occupancy: Event-by-event baseline shift dependent on input signal Few channels left to determine common mode noise correction Base line before and after correction

15. Signal to Noise Ratios

16. Tracking dE/dx resolution = 6.9%

17. Latchup Protection Circuitry  Trying to protect VA chips by quickly switching off strings of chips when current gradients too high  With current RHIC running this happens every 1-2 hours  Highly dependent on beam quality  If not too many strings are affected then a quick reset is possible, otherwise the silicon system has to be switched off/on  Not a single chip lost until....

18. Dead Channels after Beam Blast RingN RingP Octagon Just after the beam blasted the detector After readjusting the VA chip operating parameters

19. Broken Calibration and Dead Channels

20. Damage report  Gain Calibrations is broken for many channels  Most of the channels exhibit same mip peak after applying the old gain on beam data after blast  Amount of dead channels went from 1% to 2% (~2800 out of 137000)  Most likely huge hit signals doing damage, not the integrated radiation dose  We survived the first blast and the second and the third and.....

21. Performance Conclusions  Well understood signal response of detector (down to few % level) leads to quick and reliable physics results  Not zero suppressing was crucial for offline analysis of detector response  Very stable system until the beam gets dumped in it (1% extra dead)  Low maintenance system, turn-key operation  Happy Silicon = Happy PHysicists

22. Charm Upgrade Motivation  Charm cross-section in Au+Au@ RHIC uncertain  Hidden charm is major part of RHIC program  Total charm production essential normalization  Hidden charm/open charm is O(0.01)  Gap in RHIC experimental program  no true micro-vertexing so far (3-inch beampipe)

23. Charm facts  dN/dy (cc) in central Au+Au @ RHIC approx. 1 (PRL 81(1998) 1801)  Decay length: ¥ 0.13mm for D 0 (m=1.86 GeV) ¥ 0.32mm for D +/- (m=1.87GeV)  Channels (BR O(5%)) ¥ D -> K+pi ¥ Full kinematic reconstruction of D mesons ¥ Needs large acceptance ¥ D -> (di-)muon(s) + X ¥ D -> electron + X ¥ Best suited for small acceptance near mid-rapidity

24. Schematic Upgrade Layout Electron-ID Micro-Vertex EM-Calorimeter

25. Statistics (resolution, hadron rejection)  Assume >10 3 pion rejection at 90% e +/- efficiency  Assume <20 micron point resolution in y,z  O(10 4 ) electrons from charm per RHIC year (after ID+acceptance cuts) 1 RHIC year, PHOBOS acc.

26. uVertex Layout Beam Beam

27. uVertex module Plenty of space for:  Hybrids  Mechanics  Cooling

28. uVertex option I  Use the existing PHOBOS Silicon Pad technology  Advantages:  Well known sensor technology  Identical hybrids/chips(rad.tol.)  Identical readout system  Disadvantages:  Granularity limited by chip density  50um x 6.5mm strips  2 back-to-back sensors needed to get sufficient spatial resolution  2 different sensor types

29. uVertex option II  Use the ALICE Pixel Detectors  Advantages:  50um x 500um pixels  1 sensor gives 1 spacepoint  Well established design  Disadvantages:  Different sensor technology  Assembly different from current design  'Out of House' production  Different readout system

30. The PHOBOS Advantage  Complementary to charm capabilities of other experiments  Timely and cost-effective implementation (2003-2004)  Smooth transition from existing PHOBOS apparatus and physics program  Leverage existing facilities and detectors within extended collaboration