1. Fumihiko Ukegawa University of Tsukuba, Japan 6th Joint Korea-Japan ScEcal Meeting September 3, 2010 Kobe University Photo-sensor studies

2. MPPC and its linearity It saturates, by definition, at N fired = N totoal pixels

3. MPPC and its linearity : naively thinking It saturates, by definition, at N fired = N total pixels Output Input In reality, things are more complicated !!

4. Reality : FNAL test beam data Output extends way beyond N total N total pixels = 1600 LED irradiation 1600

5. On the test bench, as well Again, output exceeds N total N total pixels = 1600 Irradiate scintillator with laser 1600

6. Extended linear response because of : LED and Scint+WLS are not particularly fast, of order 10 - 30 ns MPPC pixels have a quick recovery time - A fired pixel won’t remain dead for long. It can fire again after, say, 4 ns. If the next photon comes after that, it can again give an output, and contribute to Q out So it depends on the time structure of incident photons What you think is happening : Pixels fire multiple times within the duration of a given pulse, and contribute to the extended linearity

7. If you put in a very short pulse, it should saturate at N tot Output Input Use a fast light source and measure it !

8. Hamamatsu pico-second pulser and laser : PLP-10 Catalog spec: ~70 ps pulse width, << 4 ns recovery time Detect the same light with PMT, use as a reference for the amount of light injected.

9. Need to scan a wide range in the amount of light Insert a polarizing plate between the laser and MPPC/PMT Laser light is polarized (at least partially) Rotating the plate can control the amount of light transmitted Semi-automatic, scans relatively quickly In steps of 4.5 degrees

10. Setup Clock Generator NIM Fixed DELAY Laser Source CAMAC RELAY NIM Fixed DELAY Gate Generator Thermostatic chamber( 常温 ) Polarized Controller Gate Analog CAMAC ADC H.V Power Supply 700V Voltage Power Supply Over 3V MPPC out in 200ns polarizing plate PC RS232C PCI Discriminator

11. Setup 11 PMT MPPC Filter Laser Polarizer

12. Scope photos 12 PMT MPPC GATE

13. Rotating the polarizer : Controlling the amount of light 13 PMTMPPC Rotation steps (4.5 degrees) Pulse heights (ADC counts) as a function of the angle Sinusoidal behavior for PMT

14. Converting to the number of pixels fired 77.2 V

15. MPPC vs. PMT (example) PMT Pulse Height (ADC counts) Seems to be saturating where it should be ! 1626

16. Repeat 30 times : same piece PMT Pulse Height (ADC counts) Reproducibility reasonably good

17. Same single piece, but remove from the socket and re-insert, 10 times Even better(?) reproducibility PMT Pulse Height (ADC counts)

18. Try different pieces : total of 10 PMT Pulse Height (ADC counts) p0 are the same, but p1 seem to vary from a piece to another

19. Red : single sample, just repeated 30 times Pink : single sample, removed and re-inserted, 10 times Blue : 10 different samples

20. Summary

21. To do :

22. Backup

23. PMT linearity : HV curve PMT HV （ V ） PMT pulse height (ADC counts) [0]*pow(x,[1]) 図より７００ V に設定しまし た。 （ fit 範囲の真ん中で妥当な 値）

24. d Pedestal 1p.e. 2p.e. 3p.e. 4p.e. Gain measurements Clock Generator Gate Generator Voltage source Voltage source LED driver ADC Gate Analog In Delay AMP×63 Thermostatic chamber LED MPPC PC CAMAC Width 55ns 1kHz Setup Pulse height distribution Light source : LED (green)

25. Single piece, 30 times 0.7% RMS / Mean Measurements

26. 26 4.3% RMS / Mean Measurements Single piece, 30 times

27. 27 Single piece, re-inserted 10 times Measurements 0.7% RMS / Mean

28. 28 Measurements 4.4% RMS / Mean Single piece, re-inserted 10 times

29. 29 10 different pieces Measurements 0.7% RMS / Mean

30. 30 Measurements 12% RMS / Mean  Piece-to-piece variation. Of what? 10 different pieces