M.Taguchi and T.Nobuhara(Kyoto) HPK MPPC(Multi Pixel Photon Counter) status T2K280m meeting

Test Procedure ・ Observe the raw signal ・ Confirm the fundamental performance ・ gain ・ noise rate ・ crosstalk ・ PDE(photo detection efficiency) ・ Linearity ・ Confirm the performance under the real experimental environment - scintillator+WLS fiber+MPPC ・ Laser Test (using BELLE laser system) Already presented at the previous 280m meeting Talk at this meeting

MPPC type used in each measurement measurementMPPC or Russian SiPM type CrosstalkHPK 100pixel HPK 400pixel PDEHPK 100pixel LinearityHPK 100pixel BeamtestHPK 100pixel Russian 600pixel Laser testHPK 100pixel We studied the property of HPK100pixel type in detail because we used this type of MPPC in beamtest

Crosstalk measurement Crosstalk ‥ photons emitted from one pixel during the Geiger discharge causes the Geiger discharge at neighboring pixels 0.5p.e 1.5p.e ・ Assuming 2p.e noise is caused by crosstalk of 1p.e noise(accidental coincidence of 1p.e noise is negligible) Crosstalk rate = Crosstalk rate Data taken by random trigger HPK100 HPK (V) (kHz) Maximum crosstalk rate is 0.16(HPK100) and 0.25(HPK400)

PDE=ε pixel ×QE×ε Geiger PDE(photon detection efficiency) A ratio of active area to total area (30%~70%) Quantum efficiency of active area (60~80%) Probability of Geiger discharge (60~80%) Depending on MPPC type Depending on wavelength of injected light Depending on bias V ・ PDE(photon detection efficiency) is defined as the ratio of the number of output p.e to the number of injected photons Measured the relative PDE to that of PMT with the following set up (about four HPK100 MPPCs)

PDE measurement 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 ・ change MPPC bias V ・ light sources are blue LED and wavelength shifting fiber(Y11) Blue LED WLS fiber

2mm MPPC X scanMPPC Y scan Measure PDE at this point PDE measurement(cont ’ d) ・ The max green PDE is about 1.4 times larger than that of PMT and green PDE is larger than blue PDE PDE(MPPC)/ PDE(PMT) green blue HPK100# Bias V(V) Noise rate(kHz) ・ The width of scan is 2mm ×1.4

PDE measurement(cont ’ d) ~0.8mm ・ There is a distance(~0.8mm) between surface cover and active area in HPK ’ s MPPC ・ so PDE should decrease effectively when using a WLS fiber because light from a WLS fiber spreads at 40° ½ inch PMT MPPC(total area 1mm 2 ) WLS fiber(1mmφ) Blue LED ・ Measured the effective PDE with this set up about four HPK100e MPPCs(the method of measurement is the same as before) 40° 1mm ・ compare the PDE measured in the previous measurement

PDE measurement(cont ’ d) 3mm PDE(MPPC) /PDE(PMT ) MPPC X scanMPPC Y scanEffective PDE PDE 54% ・ The width of scan becomes 3mm due to spread of light from a WLS fiber ・ The decrease of PDE due to spread of light from a WLSF is 40~50% about four HPK100 MPPCs Bias V(V) Noise rate(kHz) Effective PDE can be increased by improvement of packaging HPK100#14

Linearity measurement(HPK100) Blue LED PMT(1/2 inch PMT) MPPC (HPK100) uniform light ・ inject uniform light from blue LED to PMT and MPPC ・ monitor the light injected to MPPC by PMT ・ examine the linearity of MPPC output against PMT output ・ linearity depends on the crosstalk rate and the number of pixels, so we measured the linearity at the point that crosstalk rate is 0.03 and 0.2 Set up

Linearity measurement(cont ’ d) 10% 20% 10% 20% Crosstalk rate 0.03 Crosstalk rate 0.2 Theoretical curve calculated with the crosstalk rate and the number of pixels Difference from the linear extrapolation 50p.e injected p.e 35p.e Fired pixel number ・ data points agree well with the theoretical curve ・ HPK100(100pixel) showed 20% nonlinearity when 35~50p.e are injected (depending on crosstalk rate)

in Nov ch MAPMT (as reference) beam Scintillator 1.3x2.5x50 cm 3 (used in K2K scibar detector) 1mmΦ fiber HPK100e or Russian SiPM 4 layers 0.5 ～ 1.4GeV/c proton & pion ～ 100 event/spill beam size 1x1cm 2 setup Motivation ・ Can the light yield for T2K near detector be obtained? (more than 5p.e for MIP)

Alignment of fiber ・ The X Y position of active area of HPK ’ s MPPC is different by each sample,so alignment of fiber is necessary by each sample X Y screw for fixing fiber MPPC fiber ・ Scan the fiber with moving stage and fix the fiber with screws at the point where MPPC signal becomes maximum About 20% loss of light yield is possible due to misalignment of fiber

’ d) ・ The measured PDE including optical contact for HPK100 and Russian SiPM are about 0.7 and 1.0 of PMT, so obtained light yield is consistent with the expectation considering the misalignment of a fiber MPPC typeMPPC p.e for MIPPMT p.e for MIPRatio of MPPC p.e with PMT(%) HPK100# HPK100# HPK100# Russian600# Russian600# We could obtain the light yield for T2K near detector

Laser test(HPK100) Motivation ・ study the response of each pixel of MPPC Feed back this information to HPK microscope Laser source λ=825nm width 50ps Moving stage 1μm pitch (x, y) Laser spot size ≒ 10μm Picture of microscope MPPC 100μm ・ Efficiency distribution within 1pixel ・ Uniformity of gain and efficiency in each pixel We studied

Efficiency distribution within 1pixel 100μm 1pixel laser 0p.e. 1p.e. 0.5p.e. Efficiency =Ratio of events more than 0.5p.e to total events efficiency ・ Scan the laser in the 10mm pitch within 1 pixel(total 100scan) Efficiency flat region of 60μm×60μm

Response of each pixel ・ Inject laser to the center of each pixel and study the response of each pixel Relative gain Relative efficiency x y x y Total 100pixel RMS/mean=3.6% RMS/mean=2.5% Response of each pixel is uniform! x y

Show 20% nonlinearity when 35~50p.e are injected → need more than 200pixel The loss of light yield due to spread of light from a WLS fiber is 40~50% → can be improved by packaging Summary The green PDE is larger than that of PMT Light yield for MIP is 10~13p.e (at the point that noise rate and gain satisfy T2K requirement) Response of each pixel is uniform About HPK100pixel MPPC

supplement

Future plan Test the new samples which recently we got (HPK say these have higher PDE than others) Study the response of each pixel more in detail with the laser system for

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 :30~75V High gain:10 5 ~10 7 MPPC characters:

Signal and p.e peak Increasing the injected light 0p.e 2p.e 1p.e 30p.e HPK100a V=48V ・ We can count the peak up to 4p.e ・ the interval between each peak completes by 4%

Summary of gain measuremnt Bias V HPK100a HPK400b RUS#20 RUS#14 RUS#23 RUS#22 HPK100d HPK100e HPK100f HPK1600a ・ Gain=3×10 5 ~2×10 7 ・ T=20° ・ The (dG/dV)depends on the capacitance of pixel

Summary of gain measurement Bias V Bias V 6×10 6 HPK100e HPK400b ・ dG/dV depends on capacitance of pixel ・ Typical gain 7×10 5 ～ 6× ×10 6 gain Russian 3536 Bias V 5×10 5 gain

Summary of noise rate measurement bias voltage (V) HPK100d HPK100e HPK100f HPK1600a bias voltage (V) noise rate (Hz) RUS#20 RUS#14 RUS#23 RUS#22 noise rate(Hz) p.e threshold by pulse height 1.5p.e threshold by pulse height 0.5p.e threshold by charge (in °

Summary of noise rate measurement Noise rate (Hz) ・ Maximum noise rate~ a few MHz ・ Noise rate increases by an order of magnitude with increasing bias V by 1V 71 HPK100e 3537 Bias V Russian Noise rate (Hz) Bias V HPK400b Bias V Noise rate (Hz) p.e threshold 1.5p.e threshold

1.2GeV1.0GeV0.9GeV 0.8GeV 0.7GeV0.6GeV 0.5GeV 1.2GeV1.0GeV0.9GeV 0.8GeV 0.7GeV0.6GeV 0.5GeV MPPC MAPMT π p P/π separation is possible P/π separation