1. Development of Multi-pixel photon counters(2) M.Taguchi, T.Nakaya, M.Yokoyama, S.Gomi(kyoto) T.Nakadaira, K.Yoshimura(KEK)

2. Contents Application of MPPC for T2K experiment device-by-device variation of gain, noise rate Calibration method summary

3. precise measurement of  disappearance search for  appearance T2K experiment J-PARC Super KamioKande main goal

4. 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

5. ItemSpec.status Area1.2×1.2mm 2 HPK now working No. of pixel100/400OK gain~10 6 OK Noise rate with 0.5p.e. threshold <1MHzOK crosstalk<5%HPK now working PDE>30%/>15%OK Timing resolultion~2,3nsOK requirement from T2K ※ PDE…. without/with including the loss of light due to current package of MPPC fiber MPPC ~0.5mm 1mm

6. 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 range We measured the device-by-device variation of gain, noise rate for seven 100 and 400 pixel samples which are the same types Motivation

7. tested samples Number of pixels Pixel pitch(μm) AreaOperating voltage Geometrical efficiency 100 1.0x1.0mm 2 69-70V64% 400501.0x1.0mm 2 69-70V55% latest samples which was delivered at this month

8. device-by-device variation ~gain~ 69.4V70.4V69.4V70.4V variation 3.0×10 6 ~3.6×10 6 @70.4V variation 9.0×10 5 ～ 1.3×10 6 @70.4V 1.0×10 6 3.0×10 6 4.0×10 5 1.2×10 6 100pixel 400pixel 20 ℃ different colors correspond to data at different samples

9. device-by-device variation ~ 0.5p.e.threshold noise rate ~ 69.4V70.4V 69.4V70.4V variation 250~650kHz@70.4V variation 150~370KHz@70.4V 100pixel 400pixel 100kHz 500kHz 100kHz 400kHz 20 ℃

10. device-by-device variation ~ noise rate as a function of V-V bd ~ V-V bd 0.52 2 100pixel400pixel 100kHz 500kHz 400kHz 100kHz V bd : breakdown voltage(derived by linearly extrapolating the gain-voltage curve to the point where gain becomes zero) V bd V Gain noise rate as a function of V-V bd takes the same value for different samples  variation of noise rate comes from variation of breakdown voltage 20 ℃

11. device-by-device variation ~breakdown voltage~ numberV bd 169.3 268.6 368.7 468.8 569.0 668.6 768.4 868.7 968.4 1068.7 numberV bd 168.5 268.4 368.6 468.3 5 668.8 7 868.2 969.1 1068.1 100pixel 400pixel variation of V bd 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 ℃

12. Calibration test Motivation Gain, 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)

13. 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

14. Calibration Method 1 gaincrosstalkPDE(MPPC)/QE(PMT) V-V bd V bd : breakdown voltage V: bias voltage gain, PDE, crosstalk are all functions of V-V bd (independent of temperature) can calibrate all parameters by monitoring only one parameter(for example, gain) different colors correspond to data at different temperatures

15. calibration constant= gain x PDE x MIP ADC counts 1- crosstalk 1 estimate the variation of V-V bd estimate the variation of PDE(V-V bd ),crosstalk(V-V bd ) 0p.e. 1p.e. LED trigger data measure the variation of gain Calibration Method 1 0p.e. 1p.e. LED trigger data gain V-V bd crosstalk PDE(MPPC)/QE(PMT) V-V bd

16. 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 MIP ADC count LED ADC count calibration constant = MIP ADC count LED ADC count cosmic rayLED Inject the light from LED with the same light intensity as MIP light yield

17. Stability of device response after calibration(100pixel) +3% -3% 20 ℃ 25 ℃ method1 +3% -3% +3% 20 ℃ 25 ℃ method2 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

18. MPPC1(100)MPPC2(100)MPPC3(400)MPPC4(400) Method12.5%2.3%3.8%3.1% Method22.5%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-V bd 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)

19. 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

20. supplement

21. measurement of gain 0p.e. 1p.e. MPPC gain = 1p.e. charge e(1.6×10 -19 ) ADC distribution blue LED

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

23. Basic performance ~crosstalk~ 10 3 10 2 10 ・ Assuming 2p.e. noise is caused by crosstalk of 1p.e noise(accidental coincidence of 1p.e noise is subtracted) Cross-talk rate = Data taken by random trigger 0.5p.e. 1.5p.e.

24. measurement of PDE MPPC(total area 1mm 2 ) ½ inch PMT 1mmφslit MPPC x Y slit PMT 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

25. 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

26. setup for calibration test

27. MPPC(Multi pixel photon coutner) 100~1000 APD pixel in 1mm 2 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:10 5 ~10 7 MPPC characters:

28. Raw signal and ADC distribution

29. Where does the requirement to MPPC come from? ItemrequirementFrom where Area1.2x1.2mm 2 To match 1.0mm fiber No. of pixel100/400To keep dynamic range up to ~100p.e. gain~10 6 To set disc. threshold with reasonable precision Noise rate<1MHzTo 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.2-3nsNot so meaningful requirement