MPPC status M.Taguchi(kyoto) T2K ND /7/7

Contents Test sample Device-by-device variation Calibration test Conclusion

Test sample latest samples which was delivered in Jan.2006 We have three samples for each type device-by-device variation is tested at the point bias V=69.0V (at this point gain~10 6, noise threshold <1MHz) Number of pixels Pixel pitch(μm) AreaOperating voltage Geometrical efficiency x1.0mm V46% x1.0mm V55% HPK now develops 100pixel sample with larger geometrical efficiency

Gain ~device-by-device variation~ 100pixel gain400pixel gain variation ~7% variation ~10% 69.0V 3×10 6 1× ℃

Noise rate ~device-by-device variation~ 69.0V 100pixel Noise threshold 69.0V vairation~30% vairation~13% 400pixel Noise threshold 700kHz 800kHz 15 ℃

PDE ~device-by-device variation~ 2 100pixel 69.0V 100pixel PDE(MPPC)/QE(PMT) 400pixel PDE(MPPC)/QE(PMT) variation ~10% variation ~20 % measure the PDE of MPPC relative to that of a PMT 15 ℃ 2

Summary of device-by-device variation 100pixel400pixel gain2.6x10 6 ~ 3.0x x10 5 ~ 9.8x10 5 Noise th 480~620 KHz750~850kHz PDE(MPPC)/ QE(PMT) 1.8~ ~2.0 T=15 ℃, bias V=69.0V Device-by-device variation is small, but it is necessary to test much larger number of samples

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 if temperature of bias voltage change MPPC Signal ∝ Gain(T,V) x PDE(T,V) x 1-crosstalk(T,V) 1 T: temperature V: bias voltage evaluate the stability of device response by two calibration methods(explain each method later)

Set up for calibration test 1inch 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 temperature chamber

Method 1 100pixel gain100pixel crosstalk 100pixel PDE(MPPC)/QE(PMT) gain, PDE, crosstalk are all functions of V-V bd V-V bd V bd :breakdown voltage (derived by linearly extrapolating the gain-voltage curve to the point where gain becomes zero) V Gain V bd

Method 1 corrected light yield = gainxPDEx MIP ADC counts 1-crosstalk 1 20 ℃ 25 ℃ measure the variation of gain(V-V bd ) estimate variation of V-V bd estimate the variation of PDE(V-V bd ),crosstalk(V-V bd ) variation of gain (100pixel)

Stability of device response(method1) +3% -3% 20 ℃ 25 ℃ corrected light yield(100pixel) device response is stable within ~3% after calibration of method 1 response of other three samples is also well calibrated

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 we can calibrate the variation of gain, PDE, crosstalk by taking the ratio of MIP ADC count to LED ADC count corrected light yield = MIP ADC count LED ADC count

Stability of device response(method2) +3% -3% +3% 20 ℃ 25 ℃ corrected light yield(100pixel) device response is stable within ~3% after calibration of method 2 response of other three samples are also well calibrated

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)

Conclusion device-by-device variation among three samples is small,  but it is necessary to test much larger number of samples calibration is possible by two methods  further test of much larger number of samples

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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:

Basic performance ~Gain~ MPPC gain = output charge from a single pixel 0p.e. 1p.e. 2p.e. 3p.e. ADC counts calculate gain from the number of ADC counts between 1p.e. and pedestal peak

Basic performance ~gain~ 3× pixel gain bias V 68.4V69.6V 1× V69.4V bias V 400pixel gain 3×10 5

Basic performance ~Noise rate~ count the rate above 0.5 and 1.5p.e. threshold without external light Noire rate measured at the 1.5p.e. threshold increases as the temperature becomes lower 68.2V 69.8V 1MHz ■ ■ ■ : 0.5p.e threshold ▲ ▲ ▲ : 1.5p.e threshold 100kHz because the cross-talk rate increases as the temperature becomes lower 100pixel Noise threshold bias V

Basic performance ~crosstalk~ ・ 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.

Basic performance ~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

Basic performance ~linearity(100pixel)~ 3080 injected p.e injected p.e. fired pixel number (Data-Exp)/Exp(%) 6 expected curve calculated from number of pixels and measured cross-talk rate

Basic performance ~linearity(400pixel)~ injected p.e injected p.e. fired pixel number (Data-Exp)/Exp(%) 6 expected curve calculated from number of pixels and measured cross-talk rate

Photoelectrons for MIP photoelectrons at 20 ℃ are about 20% smaller than that at 25 ℃  need to correct for the variation of PDE, cross-talk rate photoelectrons for MPPC3 are much smaller than that for other MPPCs  due to misalignment of a fiber to the MPPC MPPC1(100)MPPC2(100) MPPC3(400)MPPC4(400) ℃ 25 ℃

Uniformity within 1pixel RMS/mean=2% efficiency Gain RMS/mean=2% Cross-talk rate pixel

efficiency 100pixel Gain RMS/mean=3% Cross-talk rate 0.22 Uniformity of each pixel

efficiency RMS/mean=1.7% Gain RMS/mean=1.6% Cross-talk rate Uniformity within 1pixel 400pixel 0.25

RMS/mean=2.9% RMS/mean=3.4% Gain efficiency Cross-talk rate Uniformity of each pixel 400pixel 0.18

Laser test laser 1pixel spot size~ a few μm wavelength ~532nm light intensity ~a few photons 100pixel efficiency measured the geometrical efficiency( ε geom ) by scanning the laser with 0.1μm pitch efficiency is calculated from the fraction of events with more than 0.5p.e. to the total events 68μm 100μm ε geom =46% for 100 pixel ε geom =55% for 400 pixel HPK now develops new 100pixel sample with larger geometrical efficiency 100μm

Variation of 1p.e. ADC count 1p.e. ADC count changes about 20% when temperature changes from 20 ℃ to 25 ℃ MPPC1(100) MPPC2(100) MPPC3(400) MPPC4(400) 20 ℃ 25 ℃ 40hours

MPPC1(100)MPPC2(100) MPPC3(100)MPPC4(100) -3% +3% corrected light yield = MIP ADC count 1p.e. ADC count x PDE x 1 (1-cross- talk rate) Stability of light yield ~method 1~ 20 ℃ 25 ℃

Stability of light yield ~method2~ MPPC1(100)MPPC2(100) MPPC3(400)MPPC4(400) +3% -3% 20 ℃ 25 ℃ LED ADC count = corrected light yield MIP ADC count

light yield distribution for MIP is fitted with Landau distribution temperature coefficient of scintillator and fiber is very small MPPC1(100)MPPC2(100) MPPC3(400) MPPC4(400) MIP ADC count 20 ℃ 25 ℃

400pixel gain 400pixel PDE(MPPC)/QE(PMT) 400pixel crosstalk V-V bd Gain,PDE,crosstalk are functions of V-V bd