First performance results from Phobos at RHIC

1. First performance results from Phobos at RHIC Heinz Pernegger for the PHOBOS collaboration Vertex 2000

2. 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, JawLuen Tang UNIVERSITY OF ROCHESTER A. Hayes, Erik Johnson, Steven Manly, Robert Pak, Inkyu Park, Wojtech Skulski, Teng, Frank Wolfs UNIVERSITY OF ILLINOIS AT CHICAGO Russell Betts, Christopher Conner, Clive Halliwell, Rudi Ganz, Dave Hofman, 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. RHIC environment: Highest energy density ever produced in lab Au-Au collisions with total s= 25TeV About 4000 charged particle per central collision 12 June: 1st Collisions @ s = 56 AGeV 24 June: 1st Collisions @ s = 130 AGeV 5 Sept: end of first Au-Au physics run Relativistic Heavy Ion Collider

4. PHOBOS Detector

5. Phobos searches for signs of Quark-Gluon Plasma at RHIC Measures multiplicity of charged particles over full solid angle Reconstruct tracks in mid-rapidity range with low Pt threshold and identifies them Measures particle ratio/spectra, particle correlation Phobos “lives” on analog signals of our silicon detectors Multiplicity measurement use dE/dx as multiplicity estimator Spectrometer uses dE/dx method for particle identification Analog information used to reject background Analog signals partially used in pattern recognition What does Phobos measure ?

6. The Multiplicity detector • 1 layer of large silicon pad detectors “everywhere” • Count single hits or sum of analog signals in a detector area as measure of particle multiplicity • Has to deal with high occupancy (>80%) Vertex octagon

7. The silicon spectrometer • 16 layer of smaller silicon pad detectors near mid rapdity • Tracks and Identifies particles (dE/dx) in 2T magnetic field • All silicon readout with Viking VAHDR1 chips • Very high dynamic range (>100MIPs), peaking time 1.1ms 1x1mm to 0.7x19mm

8. bias bus signal lines 1.2um ONO vias 0.2um ONO p+ Implant Polysilicon Drain Resistor 300um 5kOhm nSi n+ Our silicon detectors Double Metal, Single sided, AC coupled, polysilicon biased detectors produced by ERSO, Taiwan AC coupled Pad (p-implant + metal 1 pad) polisilicon bias resistor metal 2 readout line contact hole metal 1- metal 2

9. Before installation • The full silicon detector in numbers: • 500 wafers, 1600 Viking VAHDR1 readout chips • 9 different wafer layouts produced by Miracle/Erso, Taiwan • Assembled to 240 modules with 140 000 channels • Commissioning setup (15% of full) March-July • Study environment and measure first collisions • Full installation for physics run on July 13 • 200/200 modules functional • 1082/1084 chips functional = 99.8% • In channels: 98.8% channels fully functional • Peak Signal/Noise = 13:1 to 20:1 depending on sensor layout • Original requirements : S/N>10 and full functional channels >95%

10. RHIC beams in Phobos RHIC Integrated Luminosity 65+65 GeV Integrated Luminosity B-1 PR00 Start6 Bunches Start 55 Bunches Physics Run 2000 Date Luminosity estimated using coincidence of signals in the Zero Degree Calorimeters. =10.7barn used to convert counts to luminosity.

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

12. Performance of the Multiplicity Detector Opening to Spec phi Opening to Vtx Opening to Spec Opening to Vtx Z (beam) • One high multiplicity event in the octagon • occupancy up to 80% • Color encodes pulse height

13. Dealing with high occupancy Base line before and after correction • Problems associated with high occupancy: • Few channels left to determine common-mode-noise correction • Event-by-event baseline shift dependent on input signal

14. Signal dependence on occupancy • Problems associated with high occupancy: • Gain dependence on occupancy can distort the multiplicity measurement • Multiplicity measured = • dE(meas)/<dE(part)> • Gain loss at highest occupancy: • 20% NO baseline corr. • 6% WITH baseline corr.

15. Multiplicity sensor uniformity 3.6 x 8.4 cm Smp= 93 keV +/- 3% 8.3 cm x 6.5 cm Smp= 85keV +/- 1% No substantial signal variation due to different layout (double metal line routing/ varying pad size)

16. Performance of tracking detectors Hits in SPEC Tracks in SPEC Hits in VTX 130 AGeV 130 AGeV 56 AGeV

17. Signal uniformity in Spec/Vertex T3 Smp= 85 T4 Smp=85 T5 Smp=85 T1 Smp= 90 T2 Smp=85 • Signal distrbutions for different layouts: • All signal distribution after calibration (20% effect!) • Small pads (type 1 & 2 , 1mm2) • Larger pads (type 3,4,5 10 mm2) • “strips” (vertex : 0.4x20 mm2) • Very uniform in shape and peak Inner Vtx Smp=87 Outer Vtx Smp=85

18. Uniformity within sensors +/- 2% 1 x 1 mm2 0.4 x 6 mm2 0.7 x 7.5 mm2 Relative signal variation 0.7 x 15 mm2 0.7 x 19 mm2 0.3 x 23 mm2 • Typical variation <+/-1% within sensor over large range of pad size and readout line length 0.3 x 46 mm2 Pad row (along readout lines accros sensor)

19. Signal/Noise vs sensor layout Closest to beam Signal peak [e-] =24000e- Large pads Longs readout lines (high capacitance) Noise [e-] Chip dominated base offset (ENC = 900 e-+5e-/pF @ 1.1ms)

20. Critical test of detector understanding Both distributions contain the same number of central events Points are for VTX data No correction for detector thickness Histogram is for simulated VTX signals GEANT Response from test-beam Electronics noise Shulek correction Focus on Si signal simulation (CR setup)

21. Optimizing our signal simulation • Measured dE/dx in silicon in a testbeam and verified simulation: • Measure dE/dx and distribution shape, test PID • Cover large momentum range (130MeV – 8GeV), measure p & K Data • p • K Geant

22. VTX Tracklets Two hit combinations that point to the vertex dh = h2 – h1 Good tracklets have dh<.1 Measuring charged multiplicity • SPEC Tracklets • Two hit combinations that point to the vertex • dR =  (dh2 + df2) • Good tracklets have dR<.015

23. Results :PHOBOS Measurement of Charged Particle Multiplicitynear Mid-rapidity dNch/d (||<1) at  sNN= 56 GeV: 408±12±30 dNch/d (||<1) at  sNN=130 GeV: 555±12±35 hep-ex/0007036Accepted for publication in PRL Oct 02 2000

24. Summary • The good performance allowed a very fast physics analysis • Submitted within 5 week after first recorded collision • The first publication of all RHIC experiment • Phobos successfully completed its first physics run: • 3.5 million Au-Au collisions on tape (collected mainly in 2 weeks) • Phobos silicon detector operated flawlessly • 98 % off al channels fully functional • Not a single module failure during installation and all running • Operates at S/N >15 • Phobos is well equipped for future analysis • Very uniform and well calibrated signal response • Can operate at high occupancies • Detector showed to be reliable and stable

25. Next transparencies are backup + additions

26. Readout & Calibration system • Readout with Viking VAHDR1 chips • Very high dynamic range (>100MIPs), peaking time 1.1ms • Phobos “lives” on analog signals • Multiplicity measurement use dE/dx as multiplicity estimator • Spectrometer uses dE/dx method for particle identification • Analog information used to reject background • Analog signals partially used in pattern recognition • Dedicated calibration system • Measures full gain curve for each channel (1-2/day) • Verifies functionality and normalizes gain of different detector modules and sensors

27. Derivation of dN/dh • Extract a(Z) from correlation of • Primaries in –1 < h < 1 • Measured number of tracklets 5<z<10 Number of Tracklets VTX SPEC dN/dh

28. Measuring dN/dh with tracklets • Number of reconstructed tracklets is proportional to dN/dh | |h|<1 • To reconstruct tracklets • Reconstruct vertex • Define tracklets based on the vertex and hits in the front planes of SPEC and VTX • Redundancy essentially eliminates feed-down, secondaries, random noise hits • To determine a • Run the same algorithm through the MC • Folds in detector response and acceptance

29. Pointing accuracy describes how extrapolated tracks deviate from calculated vertex. Compares well with HIJING simulation Spectrometer sits very close to vertex High resolution tracking in 6 planes gives excellent vertex resolution z x Measuring Vertex