1. R&D of MPPC for T2K experiment
PD07 : Photosensor Workshop 2007
2007/6/28 (Thu)
S.Gomi　T.Nakaya
M.Yokoyama　H.Kawamuko ( Kyoto University )
T.Nakadaira T.Murakami　(ＫＥＫ)

2. T2K experiment MAIN GOAL Kamioka Tokai search for νμ→νe appearance
precise measurement of νμ→ντ disappearance
Kamioka
Tokai

3. MPPC satisfy those requirement!
T2K experiment SK
Far detector
Near detector
MPPC satisfy those requirement!
Target
Proton beam
Requirement to photosensor…
1. Almost of near detector composed of segmented scintillator and WLS fiber. The number of total readout channels is ~60000.
1. Compact size, low cost
2. Off-axis detector placed under 0.2T magnetic field.
2. Insensitive to the magnetic field
Iron + scintillator

4. Basic performances of MPPC
　gain
　photon detection efficiency (PDE)
　noise rate
　cross-talk rate

5. MPPC output signal
We report the basic performances of MPPC samples, S MOD, 400pixel sample.
MPPC raw signal
MPPC Histogram
Pedestal
Pedestal
1PE
1PE
2PE
3PE
2PE
3PE
MPPC has good photon counting capability. We can observe 1p.e signal peak, 2p.e signal peak, …

6. ADC distribution of MPPC
Gain measurement
Definition of gain of MPPC
set up
Measuring the little light from the blue LED by MPPC.
Gain is measured by ADC distribution.
blue LED
MPPC
ADC distribution of MPPC
Pedestal
1PE
2PE
We can define gain of MPPC by this difference.
3PE

7. Result of gain measurement
Blue : 15℃　
Green : 20℃　
Red : 25℃　
Gain : 400pixel S MOD
×10^3
C/e
1×10^6
VBD V
5×10^5
Bias voltage
Bias voltage (V)
From the result of gain, Breakdown voltage (VBD) and capacitance of MPPC can be measured.

8. Result of gain measurement
From bias voltage and breakdown voltage, ΔV of each MPPCs can be measured.
Gain DV : 400pixel S MOD
×10^3
1×10^6
VBD V
5×10^5 ΔV
Bias voltage
ΔV (V)
Blue : 15℃　
Green : 20℃　
Red : 25℃　
MPPC is a high gain device.

9. PDE measurement
The ratio of p.e of MPPC to that of PMT is taken as relative PDE of MPPC.
( p.e. = # of photo electron )
set up
MPPC
MPPC
( total area 1mm2)
1.55PE
1mmφslit
1.55
0.789
=1.96
PMT
PMT
PDE = 1.96
Blue LED
0.789PE
Moving stage

10. Result of PDE measurement
Relative PDE 400pixel
Relative PDE 400pixel : ΔV
2×PMT
1×PMT
Bias voltage [V]
Over voltage [V]
PDE of MPPC is about 2 times higher than that of PMT.
Blue : 15℃　
Green : 20℃　
Red : 25℃　

11. Noise rate measurement
pedestal
MPPC Gate=800nsec
without Light source
(random gate)
free to cross-talk & after pulse
Number of pedestal event
1p.e
Poisson distribution
2p.e ・・・
estimated 1p.e value = P(1)
≠ because of cross-talk & after pulse
estimated 2p.e value = P(2)
・・・

12. Result of noise rate measurement
Noise rate [kHz] 400pixel
Noise rate [kHz] 400pixel : ΔV
500kHz
1p.e noise
2p.e noise
250kHz
Bias voltage [V]
Over voltage [V]
Blue : 15℃　
Green : 20℃　
Red : 25℃　
1p.e noise rate is small enough to the requirement of T2K(<1MHz)

13. Cross-talk & After pulse rate measurement
In this measurement, we use ADC distribution for measurement of total influences that make 1p.e signal to 2p.e signal. We cannot distinguish this 2 component.
Measurement
without light source
The number of pedestal is free to cross-talk & A.P.
Poisson distribution
The number of >2p.e : N>2p.e
( estimated by pedestal ) ||
Without Cross-talk & A.P.
The number of >2p.e : N>2p.e
( measurement ) ||
With Cross-talk & A.P.
This difference corresponds to the decrease by cross-talk & after pulse.
Cross-talk & A.P. rate is defined.

14. Result of cross-talk & after pulse rate measurement
Cross-talk & after pulse rate 400pixel
Cross-talk & after pulse rate 400pixel : ΔV
50%
25%
Vop(HPK)
Bias voltage [V]
Over voltage [V]
Cross-talk & after pulse rate is a function of ΔV.
Blue : 15℃　
Green : 20℃　
Red : 25℃　

15. Cross-talk rate & After pulse rate
we cannot distinguish those in ADC distribution.
we can distinguish those by differences of threshold in Scalar.
0.5p.e
After pulse
1.5p.e
1p.e noise
1 gate
0.5p.e
Cross-talk
1.5p.e
1 gate

16. Noise rate
The noise rate measured by scalar is not equal to the noise rate measured by ADC distribution. Why not?
　the influence of after pulse
We reject all influences that make 1p.e to 2p.e, when we measure noise rate with ADC distribution. The other hands, noise rate measured by Scalar may contain the influence of after pulse, and therefore this value is higher.
0.5p.e
In Scalar, it seem to be 2 noises.
After pulse
In ADC distribution, it seem to be 1 noise.

17. The result of noise rate by 2 method
The result by ADC distribution is smaller than the result by scalar.
By assuming this difference come from only after pulse, we can obtain after pulse rate.
1p.e Noise (kHz)
■・・・Scalar
●・・・ADC distribution

18. After pulse rate & Cross-talk rate
After pulse rate : 400pixel
Cross-talk rate [Scalar] : 400pixel
10.55%
6.64%
All 1p.e  2p.e
The influence of after pulse is larger.
6.64%
14.11%
Cross-talk
10.55%
3.08%
After pulse

19. MPPC 300 sample test 300 MPPC samples are in our hands.
Those are all 400pixel samples. (S CK)
We measured the basic performances of those 300 samples and check the device-by-device variation of their performances.
Gain
PDE
Noise rate
Cross-talk & after pulse rate

20. Set up of measurement Light source
LED
We measured 32 MPPCs at once by using the custom electronics with Trip-T
MPPC
WLS fiber +
Connector
each fiber ･･･
・・・
×32
VME
Trip-t PC

21. Set up of measurement with light source
WLS fiber
Light source
to Trip-t chip
MPPC × 32
with Plastic connector
Those are set up of measurement. MPPC is connected with fiber by plastic connector

22. Shade the light from LED
Light source
Light source for measurement
Using the light from LED(Blue)×1 defused by 2 plastic plate.
Light from LED conduct to MPPC sensitive region by WLS fiber .
Plastic connector
Cookie and WLS fiber
LED
MPPC with connector on Trip-t board
Shade the light from LED

23. Plastic connector for MPPC fiber coupling
Prototype of Connector
Fiber housing
Fiber housing
connect
MPPC housing
MPPC housing
We make the prototype of plastic connector for MPPC WLS fiber coupling. We use this connector for measurement of PDE.

24. Trip-t chip test board developed by KEK
MPPC Hole 5.3φ
（32 Mount）
Bias control
Bias control
±5VIN
155mm
190mm
190mm
65mm
In this measurement, we use Trip-t chip test board.
This board can measure 32 MPPCs at the same time.

25. Gain measurement ( 300 samples )
Gain : 400pixel 20℃ 300samples
Gain DV : 400pixel 20℃ 300samples
×10^3
×10^3
1×10^6
5×10^5
Bias voltage (V)
ΔV (V)
Gain・・・7.3~8.5×10^5
300 MPPC samples have same gain-ΔV relation.

26. Break-down voltage (20℃) (V)
Distributions of Capacitance and Breakdown voltage
Capacitance/e : 400pixel 300samples
VBD 20℃ : 400pixel 300samples
The slope of gain-(VBias-VBD) relation
~ 2V
±10%
~ 1V
Capacitance (×e 10^5)
Break-down voltage　(20℃) (V)
300 MPPC samples have same capacitance.

27. With plastic connector
Measurement of PDE
The ratio of p.e of MPPC to that of PMT is taken as relative PDE of MPPC.
( p.e. = # of photo electron )
MPPC
With plastic connector
MPPC
1.55PE
1.55
0.789
=1.96
Same light value
PDE = 1.96
PMT
0.789PE
( reference )

28. PDE measurement ( 300 samples )
PDE : 400pixel 20℃ 300samples
PDE DV : 400pixel 20℃ 300samples
3×PMT
2×PMT
Bias voltage (V)
ΔV (V)
PDE・・・1.7~2.2×PMT
300 MPPC samples have same PDE-ΔV relation.

29. Noise rate measurement ( 300 samples )
Noise rate [kHz] : 20℃ 300samples
Noise rate [kHz] DV : 20℃ 300samples
500kHz
250kHz
ΔV (V)
Bias voltage (V)
Noise rate・・・200~400kHz

30. Cross-talk & after pulse rate・・・18~23%
Cross-talk & after pulse rate measurement ( 300 samples )
cross-talk & after pulse rate : 20℃ 300samples
cross-talk & after pulse rate DV : 20℃ 300samples
50%
30%
ΔV (V)
Bias voltage (V)
Cross-talk & after pulse rate・・・18~23%
300 MPPC samples have same cross-talk & after pulse rate-ΔV relation.

31. Requirement from T2K experiment
for 300 MPPC samples (S CK 400pixel type 1mm^2)
index
Requirement
Result
Sensitive region
1.2×1.2mm2
now testing…
Number of pixels
100/400 (/mm^2) OK
Gain
~1×106
7.3~8.5×105
1PE noise rate
<1MHz
200~400kHz
Cross talk + After pulse
<5%
13~22%
Photon detection efficiency (PDE)
>1×PMT
1.7~2.2×PMT
MPPC satisfy those requirements from T2K experiment.

32. Summary
MPPC 1×1mm2 sample satisfy the requirement from T2K experiment.
The device-by-device variation of basic performances come from the device-by-device variation of breakdown voltage, except for the noise rate.
 ΔV control gain, PDE, and cross-talk rate.
Future plan
Test the new sample of MPPC that has 1.3×1.3mm2 sensitive region.

33. Back up

34. Multi-Pixel Photon Counter ( MPPC )
Multi-Pixel Photon Counter ( = MPPC ) is a new type of photo detector developed by Hamamatsu Photonics (HPK).
MPPC consists of 100~1600 small avalanche photo diodes( APD ) in 1mm×1mm sensitive region.
1pixel
6mm
MPPC
Sensitive region of MPPC
400pixel type

35. Operation principle of MPPC
Each APD pixel operate in Geiger mode. Gain is proportional to the applied voltage above the breakdown voltage( Vbd ).
In Geiger mode, the output charge Q from a single pixel is independent of the number of injected photons within the pixel.
Vbd
Extrapolated to GAIN=0 V

36. the MPPC is an excellent photon counting device
MPPC character
Combining the output from all the pixels, the total charge from one MPPC is quantized to multiples of Q .
the MPPC is an excellent photon counting device
MPPC advantages
Compact
Insensitive to magnetic field
High gain( ~106 ), low bias voltage( ~70V )
High photon detection efficiency
Low-cost
5mm
6mm

37. MPPC 100 sample test 100 MPPC samples have come.
Those are all 400pixel samples. (S MOD)
We measured the basic performances of those 100 samples and check the device-by-device variation of their performances.

38. Light Source Light source for measurement
Using the light from LED(Blue)×1 defused by 2 papers.
Distance from the MPPC is maximum.
Paper
Blue LED
Box
Check the light distribution by scanning using PMT (with window Φ1mm). PDE is defined by this distribution.
LED voltage

39. MPPC Base Board
I made new MPPC base board to fixed MPPC. 4 MPPCs can be measured by using this new board.
This board has 2 layer, readout electronics is on the downer board and upper board fix MPPC.
Readout ×4
50mm
Bias
MPPC ×4

40. MPPC Base Board Stand This stand should have complete reproducibility.
This stop the board.
By rotating, we can detaching.

41. Measurement System Those is measurement system.
Those system is stable and has good reproducibility !

42. Result of measurement of gain ( 100 samples )
Gain : 400pixel 20℃ 100samples
Gain DV : 400pixel 20℃ 100samples
Vop(HPK)
×10^3
×10^3
1×10^6
5×10^5
Bias voltage (V)
ΔV (V)
Gain・・・~8.0×10^5
100 MPPC samples have same gain-ΔV relation.

43. Break-down voltage (20℃) (V)
Distributions of Capacitance and Breakdown voltage
The slope of gain-(VBias-VBD) relation
Capacitance/e : 400pixel 300samples
VBD 20℃ : 400pixel 300samples
~ 0.4V
±2%
Capacitance (×e 10^5)
Break-down voltage　(20℃) (V)
About 100 samples, MPPC have same capacitance.

44. Result of measurement of PDE ( 100 samples )
PDE : 400pixel 20℃ 100samples
PDE DV : 400pixel 20℃ 100samples
Vop(HPK)
2×PMT
1×PMT
Bias voltage (V)
ΔV (V)
PDE・・・~1.5×PMT
100 MPPC samples have same PDE-ΔV relation.

45. Result of measurement of noise rate ( 100 samples )
Noise rate [kHz] : 20℃ 100samples
Noise rate [kHz] DV : 20℃ 100samples
Vop(HPK)
500kHz
250kHz
Bias voltage (V)
ΔV (V)
Noise rate・・・130~310kHz
Noise rate looks like contain another factor.

46. Result of measurement of cross-talk rate ( 100 samples )
cross-talk rate DV : 20℃ 100samples
50%
Vop(HPK)
25%
Bias voltage (V)
ΔV (V)
Cross-talk rate・・・~23%
100 MPPC samples have same cross-talk rate-ΔV relation.

47. Measurement of noise rate
time 1 1 1 1 2
・・・5/Time
or 6/Time 1 2 1 2
・・・4/Time
or 6/Time 3 1 2
・・・3/Time
or 6/Time
Time
Cross-talk(1p.e2p.e)
If 1p.e noise is defined as the integral value of signals over the threshold on 0.5p.e, noise rate is changed by the gate length that used in measurement.
On the other hands, P(n) is defined as the integral value of n p.e signals and if noise is defined as Σn・P(n), we cannot distinguish 2 noise from the influences of cross-talk. MPPC has cross-talk, so it is impossible to distinguish when we use ADC distribution.

48. Shade the light from LED
Light source
WLS fiber
MPPC
LED +
Connector
each fiber ･･･
Light source (image)
･･･×32
Shade the light from LED
Light Distribution measured by PMT

49. Trip-t chip Trip-t ･･･TRIgger and Pipeline with Timing
Developed by FNAL
Used in D0 experiment
Plan to use in T2K experiment
Input ch Analog signal (negative)
Output :
Total 128pins
Discri signal of each 32ch
Analog signal proportional to input signal
Analog signal proportional to the time between input signal and gate signal