Development of Multi-pixel photon counters(2)

M.Taguchi, T.Nakaya, M.Yokoyama, S.Gomi(kyoto)

T.Nakadaira, K.Yoshimura(KEK)

Contents

• Application of MPPC for T2K experiment

• device-by-device variation of gain, noise rate

• Calibration method• summary

•precise measurement of disappearance

•search for 　 appearance

T2K experiment

J-PARCSuper KamioKande

main goal

μν νeνμν

ν

Application of MPPC for T2K

• use scintillator+wave length shifting fiber for almost all near detectors

need compact & low cost photo sensor

• OffAxis detector is put under 0.2T environment

need tolerance of magnetic field

OffAxis detector

OnAxis detector

MPPC satisfy these requirements!

target

SK

ν

Item Spec. status

Area 1.2×1.2mm2 HPK now working

No. of pixel 100/400 OK

gain ~106 OK

Noise rate with 0.5p.e. threshold

<1MHz OK

crosstalk <5% HPK now working

PDE >30%/>15% OK

Timing resolultion ~2,3ns OK

requirement from T2K

※ PDE…. without/with including the loss of light

due to current package of MPPC

fiber

MPPC~0.5mm

1mm

Device-by-device variation

• Basic performance of MPPC is almost satisfactory next, device-by-device variation of basic performance

when mass production?• if variation is large, - cannot apply the same bias voltage for all MPPCs - readout electronics needs to cover more dynamic ran

geWe measured the device-by-device variation of gain, noi

se rate for seven 100 and 400 pixel samples which are the same types

Motivation

tested samples

Number of pixels

Pixel pitch(μm) Area Operating voltage

Geometrical efficiency

100 100 1.0x1.0mm2

69-70V 64%

400 50 1.0x1.0mm2

69-70V 55%

•latest samples which was delivered at this month

device-by-device variation ~gain~

69.4V70.4V69.4V 70.4V

variation 3.0×106~3.6×106@70.4V

variation 9.0×105～1.3×106@70.4V

1.0×106

3.0×106

4.0×105

1.2×106

100pixel

400pixel

•20℃•different colors correspond to data at different samples

device-by-device variation 　　　　~ 0.5p.e.threshold noise

rate ~

69.4V 70.4V 69.4V 70.4Vvariation 250~650kHz@70.4V

variation 150~370KHz@70.4V

100pixel

400pixel

100kHz

500kHz

100kHz

400kHz

•20℃

device-by-device variation ~ noise rate as a function of V-Vbd ~

V-Vbd V-Vbd0.5 2 0.5 2

100pixel

400pixel

100kHz

500kHz400kHz

100kHz

Vbd : breakdown voltage(derived by linearly extrapolating the gain-voltage curve to the point where gain becomes zero)

Vbd V

Gain

•noise rate as a function of V-Vbd takes the same value for different samples

variation of noise rate comes from variation of breakdown voltage

•20℃

device-by-device variation ~breakdown voltage~

number

Vbd

1 69.3

2 68.6

3 68.7

4 68.8

5 69.0

6 68.6

7 68.4

8 68.7

9 68.4

10 68.7

number

Vbd

1 68.5

2 68.4

3 68.6

4 68.3

5 68.3

6 68.8

7 68.8

8 68.2

9 69.1

10 68.1

100pixel 400pixel

•variation of Vbd is about 1V

a bit large! we request HPK to make this variation small

•we are going to check the variation for ~500 samples next March

•20℃

Calibration test

MotivationGain, PDE, crosstalk of MPPC are all sensitive to the temperature and bias voltage

It is necessary to calibrate the variation of gain, PDE,crosstalk when temperature or bias voltage changes

MPPC Signal ∝ Gain(T,V) x PDE(T,V) x 1-crosstalk(T,V)

1

T : temperature V : bias voltage

I will present two calibration methods　　　　　　　　　　　 (explain each method later)

Set up for calibration test

1/2inch PMT

cosmic-ray

1mm φfiber

MPPC2(100)

MPPC1(100)

MPPC3(400)

MPPC4(400)

scintillator

blue LED

• put scintillators in four layers• inserted fibers are viewed by

four MPPCs(two are 400 pixel and two are 100pixel)

• change temperature intentionally like 20℃25℃

• The same bias voltage (69.0V) is applied to four MPPCs

• two triggers(cosmic,LED)

temperature chamber

※ we used old samples for this test

Calibration Method 1

gain crosstalkPDE(MPPC)/QE(PMT)

V-Vbd V-Vbd V-Vbd

Vbd: breakdown voltage

V: bias voltage

•gain, PDE, crosstalk are all functions of V-Vbd (independent of temperature)

•can calibrate all parameters by monitoring only one parameter(for example, gain)

different colors correspond to data at different temperatures

calibration constant=

gain x PDE x

MIP ADC counts

1- crosstalk1

estimate the variation of V-Vbd

estimate the variation of PDE(V-Vbd),crosstalk(V-Vbd)

0p.e.

1p.e.LED trigger data

measure the variation of gain

Calibration Method 1

0p.e.

1p.e.LED trigger data

gain

V-Vbd

crosstalk

PDE(MPPC)/QE(PMT)

V-Vbd

V-Vbd

Calibration Method2

MIP ADC count 　∝ gain(T,V)×PDE(T,V)×

　 LED ADC count ∝ gain(T,V)×PDE(T,V)×1

1- crosstalk(T,V)

1- crosstalk(T,V)

1

MIP ADC count

LED ADC count

calibration constant =

MIP ADC count

LED ADC count

cosmic ray

LEDInject the light from LED with the same light intensity as MIP light yield

Stability of device response after calibration(100pixel)

+3%

-3%

20℃ 25℃

method1

+3%

-3%

-3%

+3%

20℃

25℃

method2

calibration constant

calibration constant

•precision of calibration is ~3% by both methods

•response of other three samples is also well calibrated

• only the errors of MIP ADC count and gain are included

hour hour

MPPC1(100)

MPPC2(100)

MPPC3(400)

MPPC4(400)

Method1 2.5% 2.3% 3.8% 3.1%

Method2 2.5% 1.3% 2.4% 1.4%

We need to

• guarantee the stability of light from LED for method 2

• measure the PDE, cross-talk rate as a function of V-Vbd before installation for method 1

Summary and discussion about calibration test

Stability of each MPPC response after calibration in RMS/mean

calibration is possible by two methods

(the precision of calibration is better for method 2)

Summary

• use of MPPC at T2K is determined • device-by-device variation among seven

samples is a bit large we request HPK to make this variation small• we are going to check the variation for ~500

samples next March

• calibration is possible by two methods it is necessary to test much larger number

of samples

supplement

measurement of gain

0p.e.

1p.e. MPPC gain = 1p.e. charge

e(1.6×10-19)

ADC distribution

blue LED

measurement of noise rate•count the rate above 0.5 and 1.5p.e. threshold without external light

0.5p.e.

1.5p.e.

Basic performance ~crosstalk~

103

102

10

・ Assuming 2p.e. noise is caused by crosstalk of 1p.e noise(accidental coincidence of 1p.e noise is subtracted)

e.p5.0thanmoreevents

e.p5.1thanmoreevents

Cross-talk rate =

Data taken by random trigger

0.5p.e. 1.5p.e

.

measurement of PDE

MPPC(total area 1mm2)

½ inch PMT

1mmφslit

MPPC x

Y

slitPMT

The view from this side

・ only the light going through 1mmφslit is detected ・ Scan the MPPC and PMT with 　moving stage and search the 　 position with maximum light 　　 yield 　・ The ratio of MPPC p.e. to 　 　 PMT p.e. is taken as relative 　 PDE of MPPC to that of PMT

WLS fiber

blue LED

Crosstalk

• assume the crosstalk takes place sequentially at the same probability

• 1p.e. looks like:1+(crosstalk)+(crosstalk)2+‥=

correction factor of crosstalk=

1

1-crosstalk

1-crosstalk

1

setup for calibration test

MPPC(Multi pixel photon coutner)

100~1000 APD pixel in 1mm2

Each pixel operates as Geiger mode

　 (independent of input light)

The output is a sum of all the APD signals Compact

Low-cost Insensitive to the magnetic

field Low bias voltage :40~75V High gain:105~107

MPPC characters:

Raw signal and ADC distribution

Where does the requirement to MPPC come from?

Item requirement From where

Area 1.2x1.2mm2 To match 1.0mm fiber

No. of pixel 100/400 To keep dynamic range up to ~100p.e.

gain ~106 To set disc. threshold with reasonable precision

Noise rate <1MHz To reduce accidental hit to TDC

crosstalk <5% To reduce the noise rate with 1.5p.e. threshold

PDE >30%/>15% To keep as large PDE as that of PMT at least

Timing resol. 2-3ns Not so meaningful requirement