Performance of new MPPC Nov. 21 Korea-Japan joint meeting Takashi Maeda Hideki Yamazaki Yuji Sudo (University of Tsukuba) --- Contents --- Measurements of basic characteristics Measurements with laser system Summary / Plans

Characteristics of the new MPPC ► Evaluate performance  Gain, Noise Rate, Cross-Talk ► Check temperature dependence  Breakdown Voltage, Pixel Capacitance ► Evaluate the Uniformity with in a sensor using microscopic laser  Efficiency, Gain

ADC distribution ► V bias ~ 77.7 V ► Temperature = 15 o C Pedestal peak 1 p.e. peak 2 p.e. peak …

Gain results S : ADC sensitivity = 0.25 pC/ADC count = 0.25 pC/ADC count A : Amp gain = 63 = 63 e : electron charge = 1.6 x C = 1.6 x C Bias voltage (V) New MPPC samples have higher gain and are operated at higher voltage than old sample 30 o C 25 o C 20 o C 15 o C 10 o C 0 o C -20 o C

Variation of Breakdown Voltage V 0 ► V0 : Breakdown voltage ► C : Pixel Capacitance ~ 0.02 pF

Noise Rate rate of avalanche signals induced by thermal electrons New MPPC samples have lower noise rate than old one 30 o C 25 o C 20 o C 15 o C 10 o C 0 o C -20 o C

Cross-talk probability ► Measured from dark noise rate ► Stable with temperature ► Increase above V over > 4 V cross-talk to adjacent pixels is caused by photons created in an avalanche 30 o C 25 o C 20 o C 15 o C 10 o C 0 o C -20 o C

Measurement by microscopic laser system

the Microscopic laser KEK ► YAG laser,  = 532 nm ► Pulse width ~ 2 nSec, rate ~ 8 kHz The MPPC

Microscopic picture of a pixel ► No difference between an old sample and new one at a rough estimate ► Difficult to match a focus  with laser light (without filters)  Diffused reflection!?  Can we perform precise scan?

ADC distribution ► Injected laser light ► Bias Voltage 78.0 Room temperature Pedestal peak 1 pix. fired peak

Laser scan - Efficiency ► 2-dimensional scan ► can see sensitive region ► Variation within a sensitive region ~ 6.3% (RMS)

Laser scan - Gain ► Gain results with same data ► Center parts have higher gain ► Variation within a sensitive region ~ 0.9 % (RMS) x10 5

Summary ► Check performance of new MPPC samples  Have greater performance than old one  Variation check is still ongoing ► We perform laser scan within a sensor Plans ► Measure other MPPC samples ► Need to measure P.D.E., Linearity ► Evaluate uniformity within a sensor  We need more measurements and analyses

Back up …

MPPC New sample

Set up for gain measurements Thermostatic Chamber Green LED MPPC Thermostatic Chamber

Pulse shape ► Bias voltage 78.0 V 1 p.e. 2 p.e.

Low powered microscopic picture

Results of the old MPPC sample