Scintillator/WLS Fiber Readout with PSiPs

1. Scintillator/WLS Fiber Readout with PSiPs Pablo Bauleo, Yvan Caffari,Eric Martin, David Warner, Robert J. Wilson Department of Physics Colorado State University International Workshop on new Photon-Detectors (PD07) Kobe, Japan. June 27nd 2007

2. Overview • Pixelated Silicon Photosensors (PSiPs) • Motivation: T2K/ND280 + ILC Detector • Bench Tests – aPeak GPDs • FNAL Beam Test – HPK MPPC & CPTA MRS • Summary R.J.Wilson

3. Motivation • Linear Collider Detector • Muon, calorimeter systems • MINOS scintillator bar w/ Y-11 WLS fiber muon system candidate • T2K Near Detector at 280 m (ND280) • Beam Monitor (NGRID), Fine-Grained Detector (FGD), Sideways-Muon Ranging Detector (SMRD), Pi-zero Detector (P0D) • P0D : 98% n interactions <19 MeV/bar; 30% <1MeV/bar • Historically CSU also motivated by Ring Imaging Cerenkov Detectors • BaBar DIRC with array of ~11,000 1” pmts and large water tank outside magnetic field • R&D on Focusing DIRC with small arrays of single UV photon sensitive solid state pixels in the magnetic field • Led to association with US developer of PSiPs (aPeak Inc.) R.J.Wilson

4. LED g180-s145-250V - ADC0 PMT Cosmic Ray/LED charge distributions • PMT (EMI 911B) response to ~ vertical cosmics rays (VCR) as a reference • Simulate with 550 nm LED (matched to peak of Y11 WLS fiber output peak) • Allows for rapid data collection • LED distribution lacks high tail of cosmic ray sample • LED settings adjusted to shift peak for range 0.2-13 VCR; shape and spectrum of true multiple VCRs unknown • ~2 MeV deposited/VCR • No absolute calibration 1 VCR  200 “photons” out of Y11 WLS MINOS/ILC-Muon bar 1 “VCR” 1 ADC ct. = 0.125 pc Mean charge ~11 pC in 300 ns gate defines unit of 1 VCR; Same PMT fitted with a mask with 1 mm diameter circular hole; placed 80 cm from 550 nm LED LED voltage (2.5 V) and pulse width (14.5 ns) adjusted to ~ replicate charge spectrum of 1 VCR (180 ns gate) Cosmics Charge (ADC bins) R.J.Wilson

5. aPeak Inc. 64-fiber Readout (16-GPD/pixel) • aPeak goal - high efficiency, high-density, compact, low-cost WLS/fiber readout primarily for non-calorimetric use • 64 x 1 mm2 fiber readout on one chip • Each pixel is a cluster of sixteen 160x160 mm2 GPDs on 240 mm centers • Geometrical efficiency for 1.2 mm diameter fiber ~ 0.36 (0.45 for 1 mm) • Signal out proportional to number of hit GPDs; allows hit threshold tuning (not optimized for calorimetry) • Very low operating bias: ~14 V 1.2 mm 10 mm 2006 R.J.Wilson

6. Single shot Average many triggers GPD Signal 500 ns 500 ns • GPD bias -14.2 V • 550 nm LED illumination • 10x linear amplifier • Setup not optimized for fast signals – intrinsic device speed much faster (aPeak) • DC offset – origin unclear, depends on bias R.J.Wilson

7. Detection Efficiency & Dark Count Rate 1.8 0.2 0.4 1.6 0.7 1.4 0.9 1.2 1.2 DE & DCR (MHz) 2.6 1 3.9 0.8 5.2 0.6 6.5 7.9 0.4 9.2 0.2 10.5 DCR 0 0 -200 -400 -600 -800 -1000 V ( mV ) th Detection Efficiency/Dark Count Rate • Dark Count Rate (DCR) from scaler of discriminated signal • Product of signal width (w) and dark count rate (DCR) reduces effective detection efficiency by factor ~ (1-w*DCR) • DEmeas = 95% for 1 VCR has 0.6 MHz DCR so 300ns gate => DEeff ~ 78% • Improve by lowering temperature • Developed computer controlled system with Peltier refrigerator LED Intensity GPD bias -14.2 V DCR 95% DE 2.6 VCR 0.9 VCR 5.2 VCR At low Vth rate too high leadssignal overlap Note: GPD signal with 10x amplifier DE = measured rate – dark rate LED rate R.J.Wilson

8. -10°C At low temp./low bias begin to see “features” -19°C Detection Efficiency: Charge Distribution DE = # triggers with charge above “threshold” # triggers -10°C Range bias voltage: 13.1-14.1 V - 1 “VCR” LED intensity () - Dark () R.J.Wilson

9. Single Photoelectron Peaks -19°C-13.3V • First time individual peaks resolved in aPeak device • Absolute gain from pe peaks ~2.5 x 106 • Dark spectrum -> crosstalk low 2 pe 3 pe 4 pe 1 pe -19°C-13.3V R.J.Wilson

10. Pixel Charge vs. Intensity • Mean measured GPD charge linear for 0-1.3 VCR; 1VCR~10pe • Plateau corresponds ~ to all 16 GPDs in the cluster registering a hit; shape consistent with a model based on earlier single GPD DE measurements; • Large “dark” charge => high rate of thermal electrons initiated signals GPD bias -14.2 VRoom temp. ( ~23°C) corrected for -29 dB attenuator but not 10x amplifier R.J.Wilson

11. aPeak GPDs Summary • New aPeak high density readout (64 fibers/chip) • Modest “calorimetric” response demonstrated; useful for threshold tuning • High efficiency for relatively high light levels at room temperature due to high dark count rate/long pulses • Low temp. demonstrated single p.e. for first time • aPeak plans • “Can reduce DCR 50-70% in medium volume run (planned for next run)” • “This will allow us to provide both verified-reliability, highly-manufacturable devices and customized devices for low-noise needs”  • “Cost/die should be similar for both technologies, however the medium volume approach would require large orders  for new layouts or if stock is depleted” • “Both technologies should provide reliable devices but only the high-volume process and layout have been (extensively) verified at aPeak for reliability and radiation damage” • Single fiber readout 129-pixel devices in-hand • Uses high volume process • Calorimetric behavior demonstrated at room temp R.J.Wilson

12. FNAL Beam Test – Experiment T695 • Cosmics give MIP response and energy scale but low rate makes it difficult to test many devices • LED flasher is fast but not the same spectrum as Y11 output and doesn’t map position response (especially in triangular P0D bars) • Beam test at new Fermi National Accelerator Lab Test Beam Facility (FTBF) – Experiment T695 • First FTBF beams delivered February 2007 and we were there just one month later – a few “hiccups” but went reasonably well. R.J.Wilson

13. Beam Parameters • 120 GeV protons (MIPs) • Timing structure • Bunch train: 84 x 18.87ns buckets in 1.58 ms • 1 train every ~12 ms (if 1 main injector bunch) • 4 sec “spill”  3.33 x 105 trains/spill • ~60,000 protons/spill • Estimate single proton per trigger ~85% of time • Beam size: • 3-4 mm RMS horizontal (along bars) • 5-6 mm RMS vertical (across the bars) • Trigger • Scintillator hodoscopes up/downstream of test box • No precision tracking in the analysis R.J.Wilson

14. CSU Beam Test Team Pablo Bauleo • DAQ/online s/w Eric Martin • Electronics David Warner • Design/fabrication Yvan Caffari • Offline analysis Robert J. Wilson • PI R.J.Wilson

15. Test Structure CSU PSiP housing;optical grease used for coupling; PMTs at far end (expect low reflection) 3 MINERVA/P0D + 2 MINOS/ILC scintillator + Y11 WLS fiber R.J.Wilson

16. Test Structure A calibrated PMT can be mounted in the same location as each PSiP “Beam Box” checkout at CSU R.J.Wilson

17. Remote controllable vertical/horizontal table FNAL Beam Test R.J.Wilson

18. Devices Tested • 5 HPK MPPC-11-T2K-5808: 400 pixel • Vop ~70 V • 4 CPTA MRS 1710: 556 pixel • 2 with Vop~44V • 2 with Vop~48V • 5 aPeak Inc. GPD 100 pixel • Vop~14 V • Not reported here R.J.Wilson

19. Calibration/Monitoring/Configurations • Monitoring pmts at opposite fiber end from PSiPs(except one) • Hamamatsu R268, Vop=1300V • Initial run through all planned beam positions with pmt replacing PSiP • Electron Tubes 9111A, Vop = -950V, gain 1.03 x 107 • “Beam Off” data (100 Hz pulser) taken interspersed with “Beam On” • “Long cables” configuration ~11ft/3.3 m cables , temp 23°C • MPPC 50Gv x 6dB attenuator; 400 ns gate • MRS 50Gv, no attenuator; 400 ns gate • “Short cables” configuration ~3ft/1 m; temp. 17°C • MPPC 50Gv, no attenuator; 200 ns gate • MRS 50Gv, no attenuator; 400 ns gate R.J.Wilson

20. y x 3 horizontal positions 3-5 vertical positions 4 y x 120 GeV/c protons 3 1 5 66 mm 40.8 mm 2 MINOS/ILC bars 3 MINERVA/P0D bars 2 FNAL Beam Test near end center far end PSiP or Calibration PMT Monitoring PMT Not to scale 4in/10cm 35in/89cm 69in/175cm To scale R.J.Wilson

21. Beam – Hodoscope 2 protons 1 proton Beam Off All plots following are “1 proton” or “Beam Off” (for pedestal/DCR) R.J.Wilson

22. The monitoring PMT has the same behavior for both runs. • So can directly compare the PSiP response to the calibration PMT Monitoring PMT MPPC Vbias = -70.0V Calibration PMT - PSiP Comparison Beam on the center of a MINERVA bar. 2 independent runs : • 1 run with a calibration PMT at the near end with 1 monitoring PMT at the far • 1 run with 1 MPPC at the near end and the same monitoring PMT. Monitoring PMT Calibration PMT R.J.Wilson

23. 4 3 1 5 2 PSiPs MPPC Charge Spectrum – 1 run Not to scale R.J.Wilson

24. MRS Charge Spectrum Near-end Far-end R.J.Wilson

25. Dark spectrum Dark spectrum 0 p.e. 0 p.e. 1 p.e. 1 p.e. 2 p.e. 2 p.e. 3 p.e. 3 p.e. 4 p.e. 4 p.e. Calibration – Dark + Signal Spectrum • Beam Off (pulser) and Beam Ondata • MPPC: use p.e. in low intensity signal and use of the p.e. in the dark spectrum (self-calibration) • MRS: use p.e. in low intensity signal; no distinct p.e. peaks in dark spectrum • Calibration PMT: known characteristics and beam data Dark spectrum MRS Dark spectrumMPPC 0 p.e. 1 p.e. 2 p.e. 3 p.e. 4 p.e. R.J.Wilson

26. HPK MPPC : Cross-talk 0.5 p.e. 1.5 p.e. # events above 1.5 p.e threshold Cross talk = # events above 0.5 p.e. threshold (no subtraction of random coincidences) R.J.Wilson

27. HPK MPPC : Gain curve ND280 electronics req. • From just beam off dark spectrum (similar results with signal spectrum) • Linear - Slope ~ 4.5 x 105 /V • => self-calibration • From fit to data – no crosstalk correction • Measured Npe ~ linear w/ V=(Vbias-Vbd) • “kink” at 3rd point – not understood… R.J.Wilson

28. HPK MPPC : Dark Rate • Dark Count Rate calculated from Beam Off spectrum for 0.5 p.e. & 1.5 p.e. thresholds • Compare with manufacturer data • Gain measurements consistent (to 10%) • > 0.5 p.e. rates lower 10-30% • > 1.5 p.e. rates higher by factor 5-7 • Effect of high crosstalk R.J.Wilson

29. CPTA MRS : Gain/Npe ND280 electronics req. # pde increase linear with V • From signal spectrum • Gain ~ linear with V=(Vbias-Vbd) • Slope ~ 3.8 x 105 /V R.J.Wilson

30. Attenuation –PMT on MINOS+MINERVA Beam on vertical center of middle MINERVA bar MINERVA/P0D MINOS Bars indicate RMS of distributions R.J.Wilson

31. Attenuation – MPPC/MRS on MINOS bar • Beam on vertical center of MINOS bar • From fit to data – no crosstalk correction (30-35% for MPPC) MPPC MRS c.f. PMT range 14.5 p.e. – 6 p.e. R.J.Wilson

32. Attenuation –MPPC/MRS on MINERVA/P0D bar • Beam on vertical center of MINERVA/P0D bar • From fit to data – no crosstalk correction (30-35% for MPPC) MPPC MRS c.f. PMT range 13 p.e. – 5.5 p.e. R.J.Wilson

33. Attenuation Summary • MPPC and MRS bias chosen to meet T2K/ND280 electronics gain & DCR requirements • MPPC_54: V=70.3V, Vop-Vbr =1.67V, Gain=822k, Xtalk=30% • MRS_111: V=42.5, Vop-Vbr=2.2V, Gain=738k • Fit to an exponential, signal at end of 240 m P0D bar would be: • 5.9 p.e. for MPPC • 2.4 p.e. for MRS • 3.5 p.e. for PMT • P0D simulation assumes 6.5 p.e. for blackened fiber end (~3.3 p.e./MeV) MPPC – xtalk corrected PMT MRS R.J.Wilson

34. Summary • US developer (aPeak) with high density, (potential) low cost design • 64 fiber r/o with modest dynamic range (16-pixels) • Room temp. operation but single p.e. resolution only below -10°C • Recent 100-pixel single fiber r/o device tested • Future developments include lower DCR design (room temp. p.e.?) • Beam test of HPK/MPPC and CPTA/MRS with MINOS & T2K/ND280 P0D bars • Beam test conditions i.e. many noise sources, long cables etc. • Evaluated basic performance characteristics • MPPC promising for QE & single p.e. DCR but crosstalk worrisome • MRS older design – PDE not high enough for P0D • T2K/ND280 committed to PSiPs rather early in their commercial history - a bold choice not without risks… continued testing is essential R.J.Wilson