1. MPPC update including plastic connector T2K experiment collaboration meeting 2007/4/18 (Wed) S.Gomi T.Nakaya M.Yokoyama ( Kyoto University ) T.Nakadaira ( ＫＥＫ )

2. 2 1. 100 MPPC test gain photon detection efficiency (PDE) noise rate cross-talk rate

3. 3 Measurement of gain pedestal 1p.e signal 2p.e 3p.e 4p.e … Definition of gain of MPPC ADC distribution MPPC No.50 15 ℃ 69.7V We can define gain of MPPC by this difference. V V BD 0 ΔV Bias voltage

4. 4 Gain  V : 400pixel 20 ℃ 100samples Gain : 400pixel 20 ℃ 100samples ~7×10^5 ~10×10^5 ×10^3 Result of measurement of gain ( 100 samples ) 100 MPPC samples have same gain-ΔV relation. 1×10^6 69 70 71 0.5 1 1.5 2 2.5 Bias voltage (V)ΔV (V)

5. 5 ±2% Capacitance/e : 400pixel 100samples VBD 20 ℃ : 400pixel 100samples Distributions of Capacitance and Breakdown voltage  Difference of gain come from difference of V BD. About 100 samples, MPPC have same capacitance.  Difference of gain come from difference of V BD. 5 5.5 6 68 68.5 69 69.5 Capacitance (×e 10^5) Break-down voltage (20 ℃ ) (V) ~ 0.4 V ~ 1.5 V The slope of gain- ΔV relation

6. 6 Measurement of PDE paper Blue LED HV ( 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 )

7. 7 PDE : 400pixel 20 ℃ 100samples PDE  V : 400pixel 20 ℃ 100samples ~1.37 ~1.80 1×PMT 69 70 71 0.5 1 1.5 2 2.5 ΔV (V) Result of measurement of PDE ( 100 samples ) 100 MPPC samples have same PDE-ΔV relation. Bias voltage (V) Difference of PDE come from difference of V BD 2×PMT

8. 8 Measurement of noise rate Number of pedestal event Poisson distribution MPPC No.050 Gate=800nsec without Light source MPPC No.050 Gate=800nsec without Light source pedestal 1p.e 2p.e ・ ・・ free to cross-talk estimated 1p.e value = P(1) estimated 2p.e value = P(2) ≠ because of cross-talk

9. 9 Noise rate [kHz] : 20 ℃ 100samples Noise rate [kHz]  V : 20 ℃ 100samples ~190kHz ~365kHz 300kHz 69 70 71 0.5 1 1.5 2 2.5 ΔV (V) Result of measurement of noise rate ( 100 samples ) Noise rate looks like contain another factor. Bias voltage (V)

10. Measurement of cross-talk rate The number of pedestal is free to cross-talk Poisson distribution The number of >2p.e : N >2p.e ( estimated by pedestal ) || Without cross-talk The number of >2p.e : N >2p.e ( measurement ) || With cross-talk measurement In this measurement, we define cross-talk as all events that make 1p.e signal to 2p.e signal. (This definition of cross-talk include the influences of after pulse.) The cross-talk rate is determined. This difference corresponds to the decrease by cross-talk.

11. 11 cross-talk rate : 20 ℃ 100samples cross-talk rate  V : 20 ℃ 100samples ~18 % ~29 % 30% 69 70 71 0.5 1 1.5 2 2.5 ΔV (V) Result of measurement of cross-talk rate ( 100 samples ) 100 MPPC samples have same cross-talk rate-ΔV relation. Bias voltage (V) Difference of cross-talk rate come from difference of V BD

12. 12 The influence of “1p.e  2p.e” In this measurement the definition of cross-talk contain the influence of after pulse. Those 2 are unable to distinguish in ADC distribution. 1p.e noise 0.5p.e 1.5p.e 0.5p.e 1.5p.e Those 2 are able to distinguish by Scalar measurement. 1 gate After pulse Cross-talk

13. 13 After pulse rate & Cross-talk rate  The influence of after pulse is larger. 10.55% 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% Please refer to the presentation in March Photosensor Meeting for details.

14. 14 2. Plastic connector for MPPC fiber coupling connect Fiber housing MPPC housing Fiber housing MPPC housing Prototype of Connector Further tune necessary !

15. 15 Summary The device-by-device variation of basic performances come from the device-by-device variation of breakdown voltage. –Noise rate, however, looks like contain another factor. We obtain the prototype of plastic connector.  We have to start tuning and testing.  ΔV control gain, PDE, and cross-talk rate.

16. 16 Back up

17. 17 Trip-t chip test board for T2K experiment Trip-t MPPC signal input That is the one of the purposes for this measurement, to confirm whether 16 MPPCs those basic performances become complete can be chosen. Trip-t chip, that can be used for reading out signals from many MPPC at same time was used in this measurements. Trip-t is planed to use in T2K experiment. In T2K experiment, signals from 16 MPPCs are read out by 1 Trip-t chip.

18. 18 2p.e noise rate We can define 1p.e noise rate. When we measure noise rate by ADC distribution, however, we cannot distinguish the influences of 2p.e noise rate from all influences those make 1p.e signal to 2p.e signal. We cannot define 2p.e noise rate 1p.e noise 0.5p.e 1.5p.e 0.5p.e 1.5p.e we can distinguish those by differences of threshold in Scalar. we cannot distinguish those in ADC distribution. 1 gate After pulse Cross-talk

19. 19 Light source Light source in this measurement –Shade off the light from blue LED×1. –Separate light source and MPPC as possible. paper Blue LED Scan by PMT(Φ1mm) and measure the value of light that inject to each MPPCs.

20. 20 Measurement of PDE We define PDE by the ratio of the value of light that inject each MPPCs measured by PMT. (relative PDE) 。 We set another MPPC for reference and check the stability of light source. Position 1+24mm Position 2+14mm Position 3-14mm Position 4-24mm Result of scanning by PMT

21. 21 MPPC base board We make new base board for this measurement that can fix each MPPCs in each points. We can measure 4 MPPCs at same time. This base board has 2 layer. Read out electronics set on under layer, and top layer fix MPPCs. HV Read out ×4 MPPC ×4 50mm

22. 22 MPPC base board stage It must have reproducibility. Stop by this point. Put and remove MPPCs

23. 23 Set up of this measurement Set up of this measurement. Light source is stable because we never touch this. MPPC base board stage is also stable because it is heavy. In this measurement, we did not use movement stage because it is one of the origin of noise.

24. 24 Gain : 400pixel No.50 Gain  V : 400pixel No.50 Gain  V : 400pixel 20 ℃ 100samples Gain : 400pixel 20 ℃ 100samples ×10^3

25. 25 The relation between Breakdown voltage and HPK recommendation voltage (400pixel) Vop (HPK) versus VBD we can estimate breakdown voltages from data of HPK recommendation voltage. blue : 15 ℃ blue : 15 ℃ green : 20 ℃ green : 20 ℃ red : 25 ℃ red : 25 ℃ Gain of MPPC is about 7×10^5(@25 ℃ ) in HPK recommendation voltage. We plot HPK recommendation voltage in horizontal axis, and breakdown voltage at each temperature in vertical axis.

26. 26 PDE : 400pixel No.50 PDE  V : 400pixel No.50 PDE : 400pixel 20 ℃ 100samples PDE  V : 400pixel 20 ℃ 100samples

27. 27 Noise rate [kHz] : 400pixel No.50 Noise rate [kHz]  V : 400pixel No.50 Noise rate [kHz] : 20 ℃ 100samples Noise rate [kHz]  V : 20 ℃ 100samples

28. 28 cross-talk rate : 400pixel No.50 cross-talk rate  V : 400pixel No.50 cross-talk rate : 20 ℃ 100samples cross-talk rate  V : 20 ℃ 100samples

29. 29 Measurement of noise rate 1111 121 31 ・・・ 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 2 2 2 or 6/Time Cross-talk(1p.e  2p.e)

30. 30 The definition of noise rate If that definition of noise rate is right, noise rate is not depend on the gate length. ■ ・・・ 800nsec ● ・・・ 200nsec 2 are corresponding Same differences come when the ΔV became high. Noise [ kHz ] : No.50 (Scalar) 800nsec & 200nsec

31. 31 Gain : 100pixel No.1 Gain  V : 100pixel No.1 Gain : 100pixel 20 ℃ 12samples Gain  V : 100pixel 20 ℃ 12samples

32. 32 C/e : 100pixel 12samples VBD 20 ℃ : 100pixel 12samples Distributions of C/e and VBD about MPPC(100pixel) 12 samples at 20 ℃ We have to measure all samples. The conclusion cannot be put now. Vop (HPK) 100pixel

33. 33 PDE : 100pixel No.1 PDE  V : 100pixel No.1 PDE : 100pixel 20 ℃ 12samples PDE  V : 100pixel 20 ℃ 12samples

34. 34 Noise rate [kHz] : 100pixel No.1 Noise rate [kHz]  V : 100pixel No.1 Noise rate [kHz] : 20 ℃ 12samples Noise rate [kHz]  V : 20 ℃ 12samples

35. 35 cross-talk rate : 100pixel No.1 cross-talk rate  V : 100pixel No.1 cross-talk rate : 20 ℃ 12samples cross-talk rate  V : 20 ℃ 12samples

36. 36 Noise rate [ kHz ] (Scalar measurement) Noise [kHz] : 400pixel No.50 Scalar Noise [kHz]  V : 400pixel No.50 Scalar Noise [kHz] : 100pixel No.1 Scalar Noise [kHz]  V : 100pixel No.1 Scalar

37. 37 cross-talk rate = (2p.e noise / 1p.e noise) cross-talk rate : 400pixel No.50 cross-talk rate  V : 400pixel No.50 cross-talk rate : 100pixel No.1 cross-talk rate  V : 100pixel No.1

38. 38 Comparison of noise rate, Scalar and ADC distribution Noise rate measured by Scalar is higher than noise rate measured by ADC distribution. 1p.e Noise [kHz] MPPC 400pixel No.50/100samples ■ ・・・ Scalar ● ・・・ ADC distribution blue : 15 ℃ blue : 15 ℃ green : 20 ℃ green : 20 ℃ red : 25 ℃ red : 25 ℃

39. Noise rate Why noise rate is differ when we measured noise rate by 2 methods, Scalar and ADC distribution?  the influence of after pulse Noise rate measured by ADC distribution is the rate of 1p.e pulse come from the Geiger discharge by thermo electron. 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.