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

2 T2K experiment MAIN GOAL search for ν μ →ν e appearance precise measurement of ν μ →ν τ disappearance T Tokai K Kamioka

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

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

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

6 Gain measurement Definition of gain of MPPC We can define gain of MPPC by this difference. 1PE 2PE 3PE Pedestal 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

7 Gain : 400pixel S MOD ×10^3 Result of gain measurement From the result of gain, Breakdown voltage (V BD ) and capacitance of MPPC can be measured Bias voltage (V) V V BD 0 Bias voltage C/e 1×10^6 5×10^5 Blue: 15 ℃ Blue: 15 ℃ Green: 20 ℃ Green: 20 ℃ Red: 25 ℃ Red: 25 ℃

8 Gain  V : 400pixel S MOD ×10^3 Result of gain measurement 1×10^ ΔV (V) 5×10^5 V V BD 0 Bias voltage ΔV From bias voltage and breakdown voltage, ΔV of each MPPCs can be measured. MPPC is a high gain device. MPPC is a high gain device. Blue: 15 ℃ Blue: 15 ℃ Green: 20 ℃ Green: 20 ℃ Red: 25 ℃ Red: 25 ℃

9 PDE measurement ( p.e. = # of photo electron ) The ratio of p.e of MPPC to that of PMT is taken as relative PDE of MPPC. 1.55PE 0.789PE PDE = 1.96 MPPC =1.96 MPPC 1mmφslit Blue LED ( total area 1mm 2 ) PMT set up Moving stage PMT

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

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

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

Cross-talk & After pulse rate measurement 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. Measurement without light source 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. Cross-talk & A.P. rate is defined. This difference corresponds to the decrease by cross-talk & after pulse.

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

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

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. After pulse 0.5p.e In Scalar, it seem to be 2 noises. In ADC distribution, it seem to be 1 noise.

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

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

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

22 Light source Plastic connectorCookie and WLS fiber LED Shade the light from LED MPPC with connector on Trip-t board 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.

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

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

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

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

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

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

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

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

31 indexRequirementResult Sensitive region1.2×1.2mm 2 now testing… Number of pixels100/400 (/mm^2) OK Gain~1× ~8.5×10 5 1PE noise rate<1MHz200~400kHz Cross talk + After pulse<5%13~22% Photon detection efficiency (PDE) >1×PMT1.7~2.2×PMT Requirement from T2K experiment MPPC satisfy those requirements from T2K experiment. for 300 MPPC samples (S CK 400pixel type 1mm^2)

32 The device-by-device variation of basic performances come from the device-by-device variation of breakdown voltage, except for the noise rate. Summary MPPC 1×1mm 2 sample satisfy the requirement from T2K experiment.MPPC 1×1mm 2 sample satisfy the requirement from T2K experiment. Test the new sample of MPPC that has 1.3×1.3mm 2 sensitive region. Future plan  ΔV control gain, PDE, and cross-talk rate.

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. MPPC 1pixel Sensitive region of MPPC 400pixel type 6mm

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

36 6mm 5mm MPPC character Combining the output from all the pixels, the total charge from one MPPC is quantized to multiples of Q. MPPC advantages –Compact –Insensitive to magnetic field –High gain( ~10 6 ), low bias voltage( ~70V ) –High photon detection efficiency –Low-cost the MPPC is an excellent photon counting device

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 LED voltage Check the light distribution by scanning using PMT (with window Φ1mm). PDE is defined by this distribution.

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. Bias Readout ×4 MPPC ×4 50mm

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

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

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

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

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

47 Measurement of noise rate ・・・ 5/Time time 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. ・・・ 4/Time ・・・ 3/Time Time or 6/Time Cross-talk(1p.e  2p.e)

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

49 Trip-t chip  Developed by FNAL  Used in D0 experiment  Plan to use in T2K experiment  Input 32ch Analog signal (negative)  Output 1. Discri signal of each 32ch 2. Analog signal proportional to input signal 3. Analog signal proportional to the time between input signal and gate signal :::: Trip-t TRIPT Trip-t ･･･ TRIgger and Pipeline with Timing Total 128pins