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
PMT Cosmic Ray/LED charge distributions
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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
Data - 1vcr_15inchhodoscope_datacut - ADC0
420
1 “VCR”
400
380
360
340
320
Gaussian
amplitude :
mean :
sigma :
290.11
89.234
12.570
Gaussian
amplitude :
mean :
sigma :
43.945
113.50
45.078
Gaussian+Gaussian
Gaussian: amplitude
Gaussian: mean :
Gaussian: sigma :
Gaussian: amplitude
Gaussian: mean :
Gaussian: sigma :
χ² :
300
280
260
240
220
: 290.11±6.24
89.234±0.26
12.570±0.301
: 290.11±6.24
89.234±0.26
12.570±0.301
1.8647
200
180
160
1 ADC ct. = 0.125 pc
140
120
LED
100
80
Mean charge ~11 pC in 300 ns gate defines unit of 1 VCR;
60
40
Same PMT fitted with a mask with 1 mm diameter circular hole;
20
placed 80 cm from 550 nm LED
0
0
LED voltage (2.5 V) and pulse width (14.5 ns) adjusted to ~
replicate charge spectrum of 1 VCR (180 ns gate)
R.J.Wilson
Cosmics
20
40
60
g180-s145-250V - ADC0
80
100
120
140
160
180
200
220
240
Charge (ADC bins)
aPeak Inc. 64-fiber Readout (16-GPD/pixel)


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aPeak goal - high efficiency, highdensity, 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
R.J.Wilson
1.2 mm
2006
Single shot
Average many triggers
GPD Signal
500 ns

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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
500 ns
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%
1.8
GPD bias -14.2 V
1.6
DE & DCR (MHz)

Detection Efficiency & Dark Count Rate
DCR
1.2
1
0.8
2.6 VCR
0.6
0.9 VCR
0.4
Improve by lowering temperature
– Developed computer controlled
system with Peltier refrigerator
5.2 VCR
At low Vth rate
too high leads
signal overlap
0.2

95% DE
1.4
0
0
-200
-400
-600
-800
LED
Intensity
0.2
0.4
0.7
0.9
1.2
2.6
3.9
5.2
6.5
7.9
9.2
10.5
DCR
-1000
Vth ( mV ) Note: GPD signal with 10x amplifier
DE = measured rate – dark rate
LED rate
R.J.Wilson
Detection Efficiency: Charge Distribution
DE = # triggers with charge above “threshold”
# triggers
-10°C
-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 ()
R.J.Wilson
Single Photoelectron Peaks
-19°C
-13.3V
1 pe
2 pe
3 pe
4 pe
-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
R.J.Wilson
GPD pixel 4-3 amplifier output, 500 ns gate
6000
GPD bias -14.2 V
Room temp. ( ~23°C)
5000
3500
4000
charge ( pC )
charge ( pC )
corrected for -29 dB attenuator but not 10x amplifier
Pixel Charge vs. Intensity
3000
2000
3000
2500
1000
0
2000
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
0.0
0.5
1.0
VCR equivalent LED output
VCR equivalent LED output

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
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
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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
David Warner
– DAQ/online s/w
– Design/fabrication
Eric Martin
Yvan Caffari
– Electronics
– 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
“Beam Box” checkout at CSU
A calibrated PMT can be mounted
in the same location as each PSiP
R.J.Wilson
FNAL Beam Test
Remote controllable vertical/horizontal table
R.J.Wilson
Devices Tested

5 HPK MPPC-11-T2K-5808: 400 pixel
– Vop ~70 V
SiPD
47 kohm
47 kohm
1
1
Bias
Signal
100 nF

4 CPTA MRS 1710: 556 pixel
– 2 with Vop~44V
– 2 with Vop~48V
SiPD
10 kohm
100 nF
1
1
Bias
Signal
100 nF

100 nF
5 aPeak Inc. GPD 100 pixel
– Vop~14 V
– Not reported here
R.J.Wilson
10 kohm
Calibration/Monitoring/Configurations
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
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
FNAL Beam Test
PSiP
near end
or
Calibration
PMT
y
center
far end
Monitoring
PMT
Not to scale
4in/10cm
35in/89cm
x
69in/175cm
3 horizontal positions
3-5 vertical positions
4
40.8 mm
x
66 mm
y
120 GeV/c protons
1
3
5
2 MINOS/ILC bars
3 MINERVA/P0D bars
2
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
Calibration PMT - PSiP Comparison
Beam on the center of a
MINERVA bar.
Calibration PMT
MPPC
Vbias = -70.0V
Monitoring
PMT
Monitoring
PMT
R.J.Wilson
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.
• The monitoring PMT has the
same behavior for both runs.
• So can directly compare the
PSiP response to the calibration
PMT
MPPC Charge Spectrum – 1 run
4
1
3
5
2
Not to scale
PSiPs
R.J.Wilson
MRS Charge Spectrum
Near-end
Far-end
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
Dark spectrum
Dark spectrum
MRS 0 p.e.
Dark spectrum
0 p.e. MPPCDark spectrum
1 p.e.
1 p.e.
2 p.e.
2 p.e.
3 p.e.
3 p.e.
4 p.e.
4 p.e.
R.J.Wilson
HPK MPPC : Cross-talk
MPPC Crosstalk
45
40
Crosstalk (%)
35
MPPC 50
30
MPPC 51
25
MPPC 54
20
MPPC 59
15
MPPC 56
10
5
0
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
Vop-Vbr (V)
0.5 p.e. 1.5 p.e.
Cross talk =
# events above 1.5 p.e threshold
# events above 0.5 p.e. threshold
(no subtraction of random coincidences)
R.J.Wilson
2
2.1 2.2
HPK MPPC : Gain curve
ND280 electronics req.
From just beam off dark spectrum (similar
results with signal spectrum)
5
 Linear - Slope ~ 4.5 x 10 /V
=> self-calibration
From fit to data – no crosstalk correction
 Measured Npe ~ linear w/ V=(Vbias-Vbd)
rd point – not understood…
 “kink” at 3


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.
From signal spectrum
 Gain ~ linear with V=(Vbias-Vbd)
5
 Slope ~ 3.8 x 10 /V
# pde increase linear with 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

Attentuation in MINERVA/P0D Bar
18.0
16.0
Npe detected
– MPPC_54: V=70.3V, Vop-Vbr
=1.67V, Gain=822k, Xtalk=30%
– MRS_111: V=42.5, Vop-Vbr=2.2V,
Gain=738k
MPPC – xtalk corrected
14.0
12.0
PMT
10.0

8.0
MRS
6.0
4.0
2.0
0.0
0
50
100
150
MPPC and MRS bias chosen to meet
T2K/ND280 electronics gain & DCR
requirements
200
Distance along Bar (cm)
R.J.Wilson
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)
Summary

US developer (aPeak) with high density, (potential) low cost design
–
–
–
–

Beam test of HPK/MPPC and CPTA/MRS with MINOS &
T2K/ND280 P0D bars
–
–
–
–

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 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