1. Development of Multi-Pixel Photon Counters(MPPC) Makoto Taguchi Kyoto University

2. Contents  Photosensor for T2K  Multi-Pixel Photon Counters(MPPC)  Basic performance  Laser test in KEK  Summary

3. Photosensor for T2K  # of channels ~60,000 and space constraint  Compact, low-cost  0.2T magnetic field  Tolerance to magnetic field Magnet Readout with scintillators and wavelength shifting fibers developed a new photodetector, “MPPC” for T2K ν T2K near detectors

4. Multi-Pixel Photon Counter(MPPC)  Semiconductor photon counting device which consists of many Geiger-mode APD pixels  We have developed with Hamamatsu Photonics since 2 years ago PMTMPPC Size~10cm6mm Voltage1000~2000V~70V Magnetic field× ○ Gain~10 6 Photon detection efficiency ~15%30~45% Excellent performance! APD pixels 1mm

5. Operation principle of one pixel quenching resistor Geiger-mode APD V bd ： Breakdown voltage V bias ： applied voltage Geiger discharge Linear mode Geiger mode quenching = C ×(V bias -V bd ) = ~10 6 x e V bias I capacitance ~200fF ~1V charge from one pixel : Q Photon charge

6. Operation principle of MPPC  Each pixel only shows whether photon is injected or not to the pixel  Output from MPPC is a sum of output from APD pixels  Signal proportional to the # of injected photons 1p.e. 2p.e. 3p.e.

7. Measurement of basic performance  Test samples ・・・ Latest (Oct.2006) 100, 400pixel  Test items ・・・ Raw signal Gain Photon detection efficiency Noise rate Cross-talk rate Linearity only shown here Basic performance of MPPC satisfies the T2K requirements? MPPC is a new photodetector Motivation @20 ℃

8. Raw signal LED 1p.e. 2p.e. output oscilloscope, ADC photon MPPC Excellent photon counting capability! 1p.e. 2p.e. 60ns 3p.e.

9. Gain 0p.e. １ p.e. Q  1.0×10 6 ~ 3.0×10 6  Linear dependence on the applied voltage  Q = C (V bias -V bd ) applied voltage(V) 1.0x10 6 3.0x10 6 Gain = Q/e

10. MPPC PMT 1mmφslit fiber LED PDE (relative to PMT) applied voltage(V)  Larger PDE with larger applied voltage  PDE is 2~3 times larger than that of PMT! = p.e.(MPPC) p.e.(PMT) Photon Detection Efficiency(PDE) Setup 3 2

11. Noise rate applied voltage(V)  Larger noise rate with larger applied voltage  1p.e. noise rate < 500kHz  2p.e. noise rate < 100kHz  MPPC emits thermal noise without external light input  Count # of pulses above the 0.5 or 1.5p.e. threshold without external light 1p.e. noise 2p.e. noise 0.5p.e. 1.5p.e. ( kHz ) 100 1p.e. noise 2p.e.noise 500

12. Inter-pixel crosstalk Photons generated during an avalanche in one pixel trigger another avalanche in neighboring pixels Crosstalk rate= 1- f estimated f observed f estimated : Fraction of 1p.e. events calculated from that of pedestal events assuming Poisson distribution f observed : Observed fraction of 1p.e. events

13. Inter-pixel crosstalk(2)  Larger cross-talk rate with larger applied voltage  Cross-talk rate < 0.4 applied voltage(V) 0.4

14. Linearity MPPC cannot count # of injected photons correctly if several photons come to the same one pixel Linearity of MPPC is intrinsically limited by a finite number of pixels paper setup MPPC PMT LED

15. Linearity(2) expected curve calculated from # of pixels and cross-talk rate # of injected p.e. # of fired pixels +10% -10% Deviation from expected curve # of injected p.e.  Response to a large amount of light is well understood within 10%

16. Laser test in KEK Check intra & inter-pixel uniformity  Important information for product development movable stage MPPC Motivation  Test items : Intra & inter pixel uniformity of gain and efficiency green laser 100um Intra-pixel uniformity Inter-pixel uniformity ・ 10um = # of total events # of events > 0.5p.e.

17. Uniformity of gain Intra-pixel Inter-pixel RMS/mean = 2.0% RMS/mean = 3.3% 100pixel

18. Uniformity of efficiency Intra-pixel Inter-pixel RMS/mean = 2.0% RMS/mean = 2.5% 100pixel

19. Summary  We have developed MPPC for T2K  100pixel  20 ℃  Intra & inter-pixel uniformity is <3.0% ItemsPerformanceRequirements Gain(1.0~3.0)x10 6 ~10 6 Photon detection efficiency 2~3 times > PMT >PMT 1p.e. noise rate100~500kHz<1000kHz 2p.e. noise rate10~100kHz<50kHz Cross-talk rate<0.4 MPPC satisfies the T2K requirements!

20. backup

21. Gain 100pixel 400pixel 15 ℃ 20 ℃ 25 ℃ V bias

22. Noise rate (kHz) 15 ℃ 20 ℃ 25 ℃ 2p.e. noise 1p.e. noise 2p.e. noise V bias 100pixel 400pixel

23. Cross-talk rate 100pixel 400pixel 15 ℃ 20 ℃ 25 ℃ V bias

24. PDE 100pixel 400pixel 15 ℃ 20 ℃ 25 ℃ V bias

25. Photon detection efficiency(PDE) PDE = ε geom x QE x ε Geiger -ε geom : Fraction of active area to total area~70% - QE : Quantum efficiency of APD ~ 70% - ε Geiger : Geiger probability(V) ~90%

26. Recovery time Time to quench an avalanche Fire all pixels by one LED and check the response to the light from another LED 100p.e. 100ns all pixels are recovered after 100ns  recovery time <100ns

27. 100pixel 400pixel +10% +20% -10% Deviation from expectation Data Expectation

28. Readout electronics Total # of readout channels ~60,000 in T2K  Need compact and multi-channel readout electronics Motivation 14mm ch1 ch2 ch32 ch1 ch2 ch32 Trip-t parallel serial # of channels 32  1 Trip-t chip produced at FNAL time Developed readout electronics with Trip-t chip

29. Readout of MPPC with Trip-t LED Test board(4ch) Readout 4 MPPCs simultaneously X4 develop 32ch Trip-t board and test a large number of MPPCs Future plan MPPC photo peaks

30. Fiber housing MPPC housing Optical connection