1. Performance of MPPC using laser system Photon sensor workshop @ KEK 2005.12.26-27 Niigata university, ILC calorimeter group Sayaka IBA, Hiroaki ONO, Paul Anthony RAMIREZ Takahiko ITIKAWA, Hitoshi MIYATA

2. Contents 1. Study of Niigata university 2. New photon sensor -- MPPC -- 3. Laser system and setup 4. Performance of first version MPPC 1. Signal 2. Pixel signal uniformity (gain & efficiency) 3. Break down voltage 5. Development of MPPC 6. Readout from scintillator using WLS fiber 7. Summary and future plan

3. Fine segmentation scintillator Read out by photon sensor 1. Study at Niigata university Present design of GLD Calorimeter We might need smaller segmentation calorimeter  Ex. 10x40x2mm strip type scinti X, Z-layer strip scinti: 10x200x2mm Tile-layer: 40x40x2mm This granularity will be checked by simulation soon

4. 2. New photon sensor --MPPC-- MPPC :Multi Pixels Photon Counter Made by HPK and under development Compact device Gain is 10 6 ~  Same level as PMT  Don’t need other amplifier Works with much lower voltage than PMT Suitable for wavelength shifter fiber Useful under magnetic field  PMT can’t work under magnetic field Type of MPPC (100pixels)  First version (First MPPC)  Type#: 1-53-1A-11 MPPC overview MPPC 100pixels (10x10pixels) ~85um ~100um

5. 3. Laser system and setup Output circuit YAG Laser Logic readout YAG Laser Wave length & power: 532nm (10mJ/cm 2 ), 1064nm (20mJ/cm 2 ) Filter : Laser intensity is down to10 -8 Trigger : from Laser system Pulse width : <10nsec Laser beam minimum spot size : <2um Precision of laser position : ±2um MPPC

6. 4. Performance of first version MPPC Rise time : ~10ns, Fall time : ~500ns + tail From the ADC graph, we calculated the Charge output of 1pixel which is ~ 2.5pc and Gain is ~1.6x10 7 for 100pixels MPPC 10mV 500nsec View from oscilloscope From ADC signal 0pixel (0photon) 1pixel (1photon) 2pixel (2photon) signal trigger

7. Signal for laser 1pixel injection Why does MPPC yield above 2pe signal from 1pixel ?  Cross talk Laser light inject other pixels avalanche electron goes to other pixels inside semiconductor Pulse Height 1photon mean 0photon mean 0pe 1pe From cross talk Efficiency = # of 0 or 1photon events # of All events Gain = PH(ADCcount)x-0.25(pc/ADCcount) 1.6x10- 19 (pc) PulseHeight = 1photon mean – 0photon mean Measurement performance

8. Pixel signal uniformity in one pixel (Position dependence between two pixels) Checked efficiency between two pixels as uniformity measurement Scanned 7points between two pixels Wavelength : 532nm Sensor bias : 49.0V Efficiency of more than 1photon event becomes minimum at the boundary line between 2pixels Efficiency vs Position ▲ : Efficiency of 0photon event ● : Efficiency of ≧ 1photon event pixel

9. Sensor signal uniformity dependent on the pixel locations Injected laser single photon to each pixel and got response Measurement conditions  MPPC : 100pixels  Sensor bias : 49.0V  Laser wavelength : 532nm, Intensity : 160  Laser hitting area is smaller than 1pixel area  Measured points are 50points that are shown as gray area ~30um ~35um Laser hitting area (smaller than 1pixel) ~85um Measured points : 50points (Gray pixels)

10. Deviation of PH (RMS) : 10% Laser long term fluctuation : ≦ 5% Pulse Height 1photon mean 0photon mean Pulse height vs Pixel position Sensor bias: 49.0V Distribution of the PH # of pixels

11. Cross sectional view (Central part) Cross section of X-axis (line-5 + line-6) and Y-axis (line-5 + line-6) which are shown in previous slide  Central part of sensor Cutting X-axis line-5▲ + line-6▲ Cutting Y-axis line-5▲ + line-6▲ X-axis line-5 +6 Y-axis line-5+6

12. Cross sectional view (Edge part) X-axis line-9 +10 Y-axis line-9+10 Cutting X-axis line-9▲ + line-10▲ Cutting Y-axis line-9▲ + line-10▲ Cross section of X-axis (line-9 + line-10) and Y-axis (line-9 + line- 10)  Edge of sensor We can see that pulse height level and deviation look same as previous slide

13. Position dependence of efficiency Compare efficiencies between 0photon events and more than 1photon events Edge of sensor shows low signal efficiency Central area of sensor has good efficiency Efficiency : 0photon Sensor bias : 49.0V Efficiency : ≧ 1photon Sensor bias : 49.0V

14. Break down voltage MPPC 100pixel MPPC works best performance under Geiger mode Enough laser beam incident (saturation was occurred at best operation voltage) If it down the voltage, some pixel become Geiger mode 48.4V Laser : same as above (saturation) 49.1V Laser : saturation ~80pe ~10pe Sensor : First MPPC100pixels (no type#) At 48.4V 100pixels 10pixels Geiger mode 90pixels Avalanche mode Break down V = Start Geiger mode V It is different break down voltage at each pixel !!

15. Efficiency : 0photon position X=8,Y=9 eff: poor position X=5,Y=6 eff: excellent position X=5,Y=10 eff: too bad 49.1V 49.0V The part of 1photon appearance is difference ->Breakdown voltage is difference Eff. Bias(V)

16. Summary of first MPPC We measured two types of Hamamatsu MPPC which are under development : 100pixels, first type PH uniformity was 10% (RMS), while laser long term fluctuation was less than 5% Central part of a sensor had good efficiency while edge part showed inefficiency in the light collection Breakdown voltage  Breakdown voltage = start Geiger mode voltage  Sensor bias depend on Efficiency  The part of 1photon appearance was difference (~100mV) at each pixel : breakdown voltage was difference, too  Best operation voltage range was delicate (~200mV)

17. 5. Development of MPPC 1-53-1A-11 (100pixels)First MPPC(100pixels) Best operation V (Best operation range) 49.9V~50.3V (<400mV) 49.0V~49.1V (<200mV) Gain (average value)1.60x10 7 (20pixels)1.41x10 7 (50pixels) Deviation of PH for each pixel 2% (RMS of 20pixels) 10% (RMS of 50pixels) Efficiency for average of all pixels 22% (50.0V, RMS of 20pixels) 59% (49.0V, RMS of 50pixels) Deviation of efficiency for each pixel 22% (50.0V, RMS of 20pixels) 66% (49.0V, RMS of 50pixels) Break down voltage range <200mV (49.9V~50.0V) at 3pixels <200mV (49.0V~49.1V) at 6pixels

18. Deviation of PH Deviation = RMS / Mean value Deviation of PH for each pixel : 10%  2%, better than first MPPC Deviation: 2% Histogram of deviation for pulse height Deviation: 10% Using 50pixels dataUsing 20pixels

19. 7. Final summary and future plan

20. Laser intensity dependence For getting the best laser intensity corresponding to 1photon injection Measurement conditions  MPPC : 100pixels  Pixel position : center (X=5,Y=6)  Laser hitting area : within the 1pixel  Wavelength : 532nm  Used filter : for laser intensity down to10 -8 We think laser intensity 160 corresponds to 1photon injection, because this value is beginning of max of 1photon and min of 0photon Efficiency of 0pe, 1pe vs. Laser intensity ● : Efficiency of 0photon event ▲ : Efficiency of more than 1photon event Laser intensity 160 for 1photon injection

21. 6. Readout from scintillator using WLS fiber We connected scintillator and MPPC through wavelength sifter fiber and tried beta ray test Measurement conditions  Scintillator : 10x40x2mm strip type  Source : 90Sr (beta-ray)  WLS fiber : Φ1.0mm, length 20cm, Y-11 (Kuraray)  Trigger : scintillator + PMT  MPPC : first MPPC (100pixels) Setup