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This presentation discusses a high-density WLS fiber readout system utilizing Pixelated Silicon Photosensors (PSiPs) for photon detectors in muon and calorimeter systems. The system underwent bench and beam tests, showing efficient performance and potential applications for linear collider detectors like T2K/ND280 and ILC.
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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
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
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
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
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
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
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
-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
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
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
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
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
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
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
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
Test Structure A calibrated PMT can be mounted in the same location as each PSiP “Beam Box” checkout at CSU R.J.Wilson
Remote controllable vertical/horizontal table FNAL Beam Test 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 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 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
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
Beam – Hodoscope 2 protons 1 proton Beam Off All plots following are “1 proton” or “Beam Off” (for pedestal/DCR) R.J.Wilson
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
4 3 1 5 2 PSiPs MPPC Charge Spectrum – 1 run Not to scale R.J.Wilson
MRS Charge Spectrum Near-end Far-end R.J.Wilson
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
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
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
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
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
Attenuation –PMT on MINOS+MINERVA Beam on vertical center of middle MINERVA bar MINERVA/P0D MINOS Bars indicate RMS of distributions 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) MPPC MRS c.f. PMT range 14.5 p.e. – 6 p.e. R.J.Wilson
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
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
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