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 27 nd 2007

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

3. R.J.Wilson 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% 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.)

4. R.J.Wilson 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 1 ADC ct. = 0.125 pc Charge (ADC bins) Cosmics g180-s145-250V - ADC0 LED 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) MINOS/ILC-Muon bar 1 “VCR”

5. R.J.Wilson 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 mm 2 fiber readout on one chip Each pixel is a cluster of sixteen 160x160  m 2 GPDs on 240  m 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

6. R.J.Wilson GPD Signal 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 Single shot Average many triggers 500 ns

7. R.J.Wilson 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) DE meas = 95% for 1 VCR has 0.6 MHz DCR so 300ns gate => DE eff ~ 78% Improve by lowering temperature –Developed computer controlled system with Peltier refrigerator Note: GPD signal with 10x amplifier GPD bias -14.2 V 95% DE 0.9 VCR 2.6 VCR 5.2 VCR At low V th rate too high leads signal overlap DE = measured rate – dark rate LED rate LED Intensity DCR

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

9. R.J.Wilson Single Photoelectron Peaks First time individual peaks resolved in aPeak device Absolute gain from pe peaks ~2.5 x 10 6 Dark spectrum -> crosstalk low -19°C -13.3V 1 pe 2 pe 3 pe4 pe

10. R.J.Wilson 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 V Room temp. ( ~23°C) corrected for -29 dB attenuator but not 10x amplifier

11. R.J.Wilson 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

12. R.J.Wilson 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.

13. R.J.Wilson Beam Parameters 120 GeV protons (MIPs) Timing structure –Bunch train: 84 x 18.87ns buckets in 1.58  s –1 train every ~12  s (if 1 main injector bunch) –4 sec “spill”  3.33 x 10 5 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

14. R.J.Wilson 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

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

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

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

18. R.J.Wilson 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

19. R.J.Wilson 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 10 7 “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

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

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

22. R.J.Wilson Calibration PMT - PSiP Comparison Calibration PMT Monitoring PMT 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. Beam on the center of a MINERVA bar. The monitoring PMT has the same behavior for both runs. So can directly compare the PSiP response to the calibration PMT MPPC Vbias = -70.0V Monitoring PMT

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

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

25. R.J.Wilson Calibration – Dark + Signal Spectrum Beam Off (pulser) and Beam On data 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 0 p.e. 1 p.e. 2 p.e. 3 p.e. 4 p.e. 0 p.e. 1 p.e. 2 p.e. 3 p.e. 4 p.e. Dark spectrum 0 p.e. 1 p.e. 2 p.e. 3 p.e. 4 p.e. Dark spectrum MPPC Dark spectrum MRS

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

27. R.J.Wilson Signal Fitting The large signal response of the PSiPs and the calibration PMT are modeled by the function f(QDC) : f(QDC) = Gaussian(QDC) + Moyal*(QDC) Takes into account the response of the devices and energy loss in the detector (scintillator bars) Most Probable Value (MVP) from fit used to calculate the response of the PSiPs in terms of pe Calib. PMT MPPC MRS

28. R.J.Wilson HPK MPPC : Gain curve From just beam off dark spectrum (similar results with signal spectrum) Linear - Slope ~ 4.5 x 10 5 /V => self-calibration ND280 electronics req. From fit to data – no crosstalk correction Measured N pe ~ linear w/  V=(V bias -V bd ) “kink” at 3 rd point – not understood…

29. R.J.Wilson 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

30. R.J.Wilson CPTA MRS : Gain/Npe From signal spectrum Gain ~ linear with  V=(V bias -V bd ) Slope ~ 3.8 x 10 5 /V ND280 electronics req. # pde increase linear with  V

31. R.J.Wilson Attenuation –PMT on MINOS+MINERVA Bars indicate RMS of distributions MINERVA/P0DMINOS Beam on vertical center of middle MINERVA bar

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

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

34. R.J.Wilson 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

35. R.J.Wilson 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