Development of Multi-pixel photon counters(2) M.Taguchi, T.Nakaya, M.Yokoyama, S.Gomi(kyoto) T.Nakadaira, K.Yoshimura(KEK) for KEKDTP photon sensor group

Contents Application of MPPC for T2K experiment Device-by-device variation of gain, noise rate Calibration of MPPC signal Summary

Application of MPPC for T2K

precise measurement of  disappearance search for  appearance T2K experiment J-PARC Super KamioKande main goal

Application of MPPC for T2K Use scintillator+wave length shifting fiber for almost all near detectors  Need compact & low cost photo sensors OffAxis detector is put under 0.2T environment  Need tolerance of magnetic field OffAxis detector OnAxis detector MPPC is the only candidate to satisfy these requirements target SK 0.2T magnet 280m 295 km

ItemRequirementStatus Area1.2×1.2mm 2 Being developed No. of pixel100/400OK Gain~10 6 OK Noise rate with 0.5p.e. threshold <1MHzOK Crosstalk<10%Being developed PDE>30%OK Timing resolultion~2,3nsOK requirement from T2K The requirement from T2K is satisfactory except for area and crosstalk

Device-by-device variation

Basic performance of MPPC is almost satisfactory We plan to use ~50000 MPPCs  Next, device-by-device variation of basic performance when mass production? If variation is large, - one MPPC is in geiger mode but other is not… - readout electronics needs to cover more dynamic range We measured the device-by-device variation of gain, noise rate for seven 100 and 400 pixel samples Motivation

tested samples Number of pixels Pixel pitch(μm) AreaOperating voltage Geometrical efficiency x1.0mm V64% x1.0mm V55% samples which was delivered at this month

device-by-device variation ~gain~ 69.4V70.4V69.4V70.4V variation 3.0×10 6 ~3.6×10 variation 9.0×10 5 ～ 1.3×10 1.0× × × pixel 400pixel 20 ℃ different colors correspond to different samples 3.0×1 0 6

device-by-device variation ~ 0.5p.e.threshold noise rate ~ 69.4V70.4V 69.4V70.4V variation variation 100pixel 400pixel 100 kHz 500 kHz 100 kHz 400 kHz 20 ℃

device-by-device variation ~ noise rate as a function of ΔV ~ pixel400pixel 100 kHz 500 kHz 400 kHz 100 kHz V bd : breakdown voltage(derived by linearly extrapolating the gain-voltage curve to the point where gain becomes zero) V bd V Gain Noise rate as a function of ΔV takes the same value for different samples  Variation of noise rate comes from variation of breakdown voltage 20 ℃ V= V - V bd VV

device-by-device variation ~breakdown voltage~ 20 ℃ 400pixel V bd 100pixel V bd V1.0V Variation of V bd is about 1V  We asked HPK to reduce the variation  Electronics is designed to be able to trim bias voltage for each MPPC We are going to check the variation for ~500 samples next March

Calibration of MPPC signal

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 when temperature or bias voltage changes MPPC Signal ∝ Gain(T,V) x PDE(T,V) x 1-crosstalk(T,V) 1 T : temperature V : bias voltage I will present two methods for calibrating MPPC signal (explain each method later)

Set up for calibration test 1/2inch 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 20 ℃  25 ℃ The same bias voltage is applied to four MPPCs two triggers(cosmic,LED) temperature chamber ※ we used old samples for this test

Calibration Method 1 gaincrosstalkPDE(MPPC)/QE(PMT) V bd : breakdown voltage V: bias voltage Gain, PDE, crosstalk are all functions of (independent of temperature) Can calibrate all parameters by monitoring only one parameter(for example, gain) different colors correspond to different temperatures V V V V V= V - V bd

calibration constant= gain x PDE x MIP ADC counts 1- crosstalk 1 Calibration Method 1 0p.e. 1p.e. gain V 1. measure the variation of gain(from 1p.e.and pedestal peak) ① 2. can estimate the variation of ② V crosstalk PDE(MPPC)/QE(PMT) ② ② V V 3. can estimate the variation of PDE( ), crosstalk( ) VV ③ ③

Calibration 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 calibration constant = MIP ADC count LED ADC count dist.taken by cosmic trig. dist.taken by LED trig. Inject the light from LED with the same light intensity as MIP light yield

Stability of device response after calibration(100pixel) +3% -3% method1 +3% -3% +3% method2 calibration constant only the errors of MIP ADC count and gain are included hour Precision of calibration is ~3% by both methods Response of other three samples is 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% Summary and discussion about calibration test RMS/mean of calibration constant Required precision is a few % (This depends on the type of detector)  Both calibration methods satisfy the requirement!

Summary MPPC is chosen as baseline photosensor forT2K near detector Performance of MPPC is satisfactory for T2K except for crosstalk and area  To be improved Variation of breakdown voltage among seven samples is 1V  We asked HPK to reduce the variation  We are going to check the variation for ~500 samples next March Developed calibration methods with ~3% precision

future plan 2007 Spring - production of 500~1000 samples - beamtest of Scinti+WLSF+MPPC Summer - decide the final spec for T2K - install MPPCs for SciBooNE experiment ? Autumn - Start mass production 2008~ detector construction 2009 Spring~ : T2K starts

supplement

measurement of gain 0p.e. 1p.e. MPPC gain = 1p.e. charge e(1.6× ) ADC distribution blue LED

measurement of noise rate count the rate above 0.5 and 1.5p.e. threshold without external light 0.5p.e. 1.5p.e.

measurement of 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.

measurement of 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 blue LED

Crosstalk assume the crosstalk takes place sequentially at the same probability 1p.e. looks like: 1+(crosstalk)+(crosstalk) 2 + ‥ = correction factor of crosstalk= 1 1-crosstalk 1

setup for calibration test

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:

Raw signal and ADC distribution

Where does the requirement to MPPC come from? ItemRequirementFrom where Area1.2x1.2mm 2 To match 1.0mm fiber No. of pixel100/400To keep dynamic range up to ~100p.e. Gain~10 6 To match readout electronics Noise rate<1MHzTo reduce accidental hits Crosstalk<5%To reduce the noise rate with 1.5p.e. threshold PDE>30%Light yield Timing resol.2-3nsNot so meaningful requirement