1 MPPC update S.Gomi, T.Nakaya, M.Yokoyama, M.Taguchi, (Kyoto University) T.Nakadaira (KEK) Nov KEK

2 Contents Ceramic package of MPPC We obtain the latest sample of MPPC this October. –Ceramic package, prepared for T2K experiment. –100pixel×10, 400pixel×10 We measured the fundamental performance of this sample. –Gain –Noise rate –Cross-talk rate –Photon detection efficiency ( PDE ) 5mm 6mm

3 Gain Blue: 15degree Green: 20degree Red: 25degree Gain 400pixel Bias voltage [V] Gain 100pixel Bias voltage [V] Gain of old sample was… –1.0×10 6 ~3.0×10 6 (100pixel) –0.4×10 6 ~1.0×10 6 (400pixel)  Gain of new sample is not so changed compared to old sample. Estimated by 1p.e signal peak.

4 The measurement of noise rate The noise rate is measured by counting the rate of signal with their height over the threshold, imposed on 0.5p.e and 1.5p.e. ( The old sample have ~1.2MHz 1p.e noise rate. ) Noise signal of 100pixel MPPC at 25 degree. ( integrated ) 1 p.e 0.5 p.e = threshold 1.5 p.e = threshold “ 1p.e noise ” “ 2p.e noise ”

5 Noise rate 1p.e noise rate is about ~0.4 MHz. (old ~1.2 MHz) 2p.e noise rate is about ~0.2 MHz. (old ~0.2 MHz) 100kHz 400kHz Bias voltage [V] Noise rate [ kHz ] 400pixelNoise rate [ MHz ] 100pixel 100kHz 500kHz Bias voltage [V] Blue: 15degree Green: 20degree Red: 25degree 1p.e noise 2p.e noise 1p.e 2p.e Improved!

6 The measurement of cross-talk rate Sensitive area of 100pixel type is enlarged by 40%.  Geometrical efficiency is increased. The separation between pixels is smaller than the old sample.  Cross-talk rate may be increased Old sample ( 100pixel ) New sample ( 100pixel )

7 The probability of cross-talk is estimated by the number of 1p.e. Measurement of cross-talk rate The cross talk rate is determined. The number of pedestal are free to cross-talk the number of each p.e is assumed to be follow the Poisson distribution The number of 1p.e : P(1) ( estimated by pedestal ) || without cross-talk The number of 1p.e : P(1) ( measured ) || with cross-talk This difference corresponds to the decrease by cross-talk. measurement

8 Cross-talk rate ( Cross-talk rate of the old sample is ~30%. )  Cross-talk rate of new sample is ~1.6 times larger than old sample. 10% 50% Cross-talk rate 400pixel Cross-talk rate 100pixel 10% 50% Bias voltage [V] Bias voltage [V] Blue: 15degree Green: 20degree Red: 25degree

9 relative PDE measurement MPPC 1mmφslit Blue LED ( total area 1mm 2 ) PMT PMT made by HPK, type H8643 set up Moving stage Geometrical efficiency is larger than that of the old sample. So, PDE of new sample should be higher. PDE relative to PMT is measured.

10 relative PDE PDE is about 2~3 times higher than that of PMT. (Old sample was ~2×PMT)  ~1.4 times larger PDE than old sample. 1 2 Relative PDE 400pixelRelative PDE 100pixel Bias voltage [V] Bias voltage [V] Blue: 15degree Green: 20degree Red: 25degree

11 Summary of measurement Old sampleNew sample Gain Noise rate(1p.e) [ kHz ] ~1200~400 Cross-talk rate ~30%~50% PDE The new sample have good performance! But, Cross-talk become worse.  feed back to Hamamatsu Improved! Improved! Become worse… About the region the gains of 2sample are same…

12 Future plan… We will check the device-to-device variation for 500 MPPCs in this ceramic package next March. So, we have to make system to test many samples. We want to measure as many sample as possible at once. –Plastic connector –Read out electronics

13 Supplements

14 Gain Blue: 15degree Green: 20degree Red: 25degree Gain 400pixelGain 100pixel VV VV

15 Blue: 15degree Green: 20degree Red: 25degree Noise rate This new sample have noise rate less than the half of old sample. 100kHz 400kHz Noise rate [ kHz ] 400pixelNoise rate [ MHz ] 100pixel 100kHz 500kHz p.e 2p.e VV VV 1p.e 2p.e

16 Cross-talk rate Cross-talk rate is a function of  V. 10% 50% 12 Delta V Cross-talk rate 400pixelCross-talk rate 100pixel 10% 50% Blue: 15degree Green: 20degree Red: 25degree VV VV

17 relative PDE PDE is a function of Delta V. 1 2 Relative PDE 400pixelRelative PDE 100pixel Blue: 15degree Green: 20degree Red: 25degree VV VV

18 Set up for measuring linearity set up MPPC The number of photons emitted to MPPC are monitored by PMT. PMT Paper ( to shade off LED light )

19 Linearity The green line shows the expectation value calculated from number of pixels. Blue: DATA plot Green: expectation Linearity 400pixel Injected photoelectron per pixel Fired pixel [ % ] MPPC can operate as linear device. ~25p.e about 100pixel type ~100p.e about 400pixel type. linear Linearity 100pixel Fired pixel [ % ] Injected photoelectron per pixel linear 25% Blue: DATA plot Green: expectation