using mppcs for t2k fine grain detector - index · university of british columbia, kyoto...
TRANSCRIPT
1
Using MPPCs for T2K Fine Grain Detector
Fabrice Retière (TRIUMF)for the FGD group
University of British Columbia, Kyoto University,University of Regina,TRIUMF and University of Victoria
2
T2K Fine Grain DetectorElement of T2K near detectorActive target for neutrino interactionElements• Plastic scintillator bar
(POPOP)2 meter long
• Light collection with Wavelength Shifting fiber
• Readout by HamamatsuMPPC
• ~10,000 channels
µ
p
1 mm Y11 fiber
0.96 mm
MPPC
ν
3
FGD physics requirements100% efficiency for MIP crossing a barParticle identification• By dE/dx for particle crossing the FGD• By range, especially for stopping protons
Large energy released (10 MIPs)• By detecting Michel positrons for stopping π+
Position resolution• Bar width & no information along the bar
Timing resolution• ~ 3ns per neutrino interaction for matching with
photons in calorimeter
4
MPPC basic parameters
Gain > 2 105
• i.e. 1PE = 2 105 e-Way above typical electronics noise
Photo-detection efficiency• Comparable or better than
PMTBut need to measure PDE for proper wavelength
S. Gomi et al. (Kyoto University)
Delta V [V]0.5 1 1.5 2 2.5
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
PDE Delta V : 400pixel No.050/100
Delta V [V]0.5 1 1.5 2 2.5200
400
600
800
1000
1200
1400
310× Gain Delta V : 400pixel No.050/100
15C20C25C
PDE relative to PMT
69.5V
69.5V
Cross-talk andAfter-pulsing free
5
Photo-electron per MIPMPPC fulfill requirements
Beam test at TRIUMF• 120 MeV/c particles
Electrons are minimum ionizingWorst case scenario• No fiber mirroring• End of the bar
More than 10 direct PE even at 69.5V• No need to run at higher voltage
Issue of Fiber-MPPC coupling still being addressed• New coupler• 1.2x1.2 mm2 MPPC
M. Bryant (UBC), P.Kitching (TRIUMF), S. Yen (TRIUMF)
6
MPPC fulfilling requirementsQuantum efficiency• For 100% efficiency need more than 10 PE per MIP
Go for at least 15 PEs per MIPEnergy resolution. Not directly a MPPC issue• Driven by photon statistics (~25% for 15 PE)
Increase quantum efficiency would helpTiming resolution. • Not a MPPC issue in principle (fast)
Dynamic range• 400 pixels provide more than 50 MIPs dynamic range
due to saturationNuisances: Dark noise, cross-talk, after-pulsing
7
Reading out MPPCs
Compromise between timing resolution and integration time• Desirable to measure all pulses continuously
during beam spill (5 µs) and about 2 muondecay constant (2.2 µs) after spill
• Chose a waveform digitization solutionUse the Switch Capacitor Array designed for Time Projection Chamber (AFTER ASIC)Fairly slow shaper (100 ns rise time)50 MHz sampling frequency512 time bin ~ 10 µs total integration time
8
Waveforms from MPPC coupled to AFTER ASIC
Laser beams
Dark noise hit
Dark noise hit
~60 PE
~20PE~5 PE
~60 PE
9
Fulfilling the dynamic range and energy resolution requirements
For calibration need to identify 1 PE peak• Noise set to 0.2 PE
Maximum dynamic range = 400 PE• After-pulsing may
increase beyond 400 pixel
ASIC noise ~ 2,000 e-• MPPC gain ~ 5 105
• 0.2 PE noise ⇒attenuate by ~50
ASIC dynamic range = 600 fC• Dynamic range 0.2 PE
to ~200 PE • Need another channel
with higher attenuation
10
Coupling AFTER ASIC to MPPC
Issues• Attenuation
High/low input to ASIC• Low input capacitance
Low electronic noise• Noise from resistors• MPPC recovery
Require small Rbias with purely capacitive termination
• Minimize reflections (50 Ω line)• Pulse shape
Solution• Not clear yet. Some answer
from Spice simulations• Building a specific 8 channel
prototype
MPPC
Charge pump70 V
10-15 cm
DAC-5V to +5V
Charge sum
Rbias ~ 100 kΩ
Cdec = 1 nF
AFTERASIC
Clow = 1 pF
Chigh = 10 pF
Cgnd = 40 pF
Rgnd = 10 kΩ
Rhigh = 0 Ω
Rlow = 0 Ω
Values of R and Care only indicative
D. Bishop, L. Kurchaninov, K. Mizouchi (TRIUMF)
11
Pulse shape and recovery
MPPC
70 V
10-15 cm
Rbias 100 kΩ
Cdec = 1 nF
Chigh = 3.3 pF
Cgnd = 100 pF
Rgnd = 10 kΩ
AFTERASIC
100 pF to ground
N. Jain (Darmouth), and T. Lindner (UBC)
12
Timing resolutionObtained by fitting waveforms• Fit rising edge only
Source of fluctuations• Photon arrival time
Fiber and scintillator decay constants
Waveform distortion• Dark noise• After-pulsing
Need to measure after-pulsing to evaluate effect
4±1 nsData + rising edge fit
5 nsData + full waveform fit
3 nsSimulations + waveform fit
Resolution for MIP (20 PE)
Configuration
T. Lindner, S. Oser (UBC)
13
Beyond the gross featuresEstimating the MPPC NuisancesDark noise• Add pulses. Increase data size
But useful for gain calibration• At <500 kHz, does not affect timing and energy
resolutionCross-talk• Marginal worsening of energy resolution (if <20%)• Increase number of PE
May skew timing resolution
After-pulsing• Worsen timing resolution when fitting full waveform
14
Measuring Dark noise, cross-talk and after-pulsing
Fast recovery biasing scheme: no resistance in seriesTrigger on Dark noise hits (~0.3 PE threshold)Use fast amplifier (CAEN N978)Use 1 GHz digitizer (CAEN V1789)Search for pulses• Extract MPPC*Amplifier response function• Search for pulses based on rise time + fall time +
amplitude criteria• Fit by a superposition of response functions
Add more pulses if poor fit (partial pulse overlap)• Pulse finding is the main source of systematic errors
15
Typical waveforms with after-pulsing test setup
2 missedpulses
Pulse addeappropriate
2.0 PE (cross-talk)
∏ Data (70V, 25C) pulse finder∏ First pass refit∏ Refit after splitting
1.06 PE @ 6490.96 PE @ 6530.90 PE @ 6693.21 PE @ 719
16
Amplitude vs timefor all pulses
Trigger pulseCross-talk = 1-N(1PE)/Ntot
70 V, 25C
17
Hit amplitude vs time70 V, 25C
Expected 8.75 ns recoverytime constant ⇒ could be lengthened
Trigger pulses
Cross-talk region
18
Reducing after-pulsing by playing with recovery time
It is possible to reduce after-pulsing by increasing the recovery time• Resistance in series with bias• Introduce dead time after the pulse
Is there an acceptable compromise?
• For the FGD, readout issue may force us to run with a long recovery time
After-pulsing is then automatically reduced
FGD approach• Run a low bias voltage: after-pulsing ~ 10%
19
Separating Dark Noise and after-pulsing
Count all hits• No cross-talk• Sensitive to
multiple after-pulse
Histogram the time of the 1st
hit after trigger• No cross-talk• No multiples
But more complicated fit
70VAll hits
69.5VAll hits
70 V1st hit after trigger
69.5 V1st hit after trigger
2 exponential fit1 exponential fit
20
After-pulsing fit results
Fit is impaired by low statistics• 69.5V and 70V have
more statistics • Long time constant
hard to pin downIncrease of constant in all hits expected
• Short time constant 20-30 ns
Dominate the after-pulsing
21
Competing contributions
Total after-pulsing
Is dark noise really saturating andthe visible increase due to after-pulsing?
22
Conclusions
MPPC + AFTER combination fulfill FGD requirementsMPPC nuisances are under control for the FGD application• After-pulsing is dominant
Run MPPC at low bias to avoid significant after-pulsingNot a problem. Quantum efficiency is large enough
Investigating interplay between recovery, pulse shape, and after-pulsing• Is there an optimum design?
23
Back-up
24
Measuring after-pulsing with gate technique
B. Kirby (UBC)
25
Measuring after-pulsing with average
techniqueAverage of all pulses1PE response function
Dark noise contribution (fit)
Average after dark noise subtractionAfter-pulsing contribution (fit)Cross-talk contribution (fit)
R. Tacik (U. Regina)
26
1st hit timing distribution fit function
tDNtt
tDN eeApDNeApApedtdN ⋅−−−
⋅− +⎥⎦
⎤⎢⎣
⎡⋅−−= ττ
τ)1(*/
DN = dark noise rateAp = After-pulsing probabilityτ = After-pulsing time constant