Study of the MPPC for the GLD Calorimeter Readout Satoru Uozumi (Shinshu University) for the GLD Calorimeter Group Kobe Introduction Performance of 1600 pixel MPPC GLD calorimeter test module Summary & Plans

International Linear Collider Various precision measurement with clean environment of the e + e - interaction –e + e - -> Higgs, SUSY, W, Z, tt … Four detector concepts are currently proposed

Particle Flow Algorithm - A powerful method for precise jet energy measurement - Momenta of charged particles in a jet (~65%) are measured by central tracker. Eneries of photons (mainly from  0, ~25%) are measured by electromagnetic calorimeter. Eneries of neutral hadrons (mainly K L 0, ~10%) are measured by hadron calorimeter. To achieve the PFA, separation of jet particles in the calorimeter is indispensable.

Sampling calorimeter with Pb/W - scintillator sandwich structure with WLSF readout Particle Flow Algorithm (PFA) requires fine granularity for the calorimeter Scintillator stirp structure Huge number of readout channels –~10M (ECAL) + 4M (HCAL) ! Used inside 3 Tesla solenoid The MPPC is feasible for the GLD calorimeter readout. The GLD Calorimeter

Required performance for the Calorimeter Gain: ~ Best to have 10 6, at least 10 5 Dynamic range: capable to measure ~1000 p.e. –MPPC is non-linear device –Number of pixels and shape of response curve are important Photon detection efficiency enough to distinguish MIP signal Dark noise rate : < 1 MHz good uniformity, small cross-talk Timing Resolution ~ 1 nsec – Necessary for bunch ID, slow neutron separation Stable against bias voltage / temperature / time No influence with 3 T magnetic field Radiation hardness

4 mm 1 x 1 mm 1.3 mm Side 3 mm The small-package 1600 pixel MPPC 1600 pixel MPPC with compact plastic package suitable for attaching to scintillator strips. Front MPPC Scintillator strip WLS fiber Side view

30 o C 25 o C 20 o C 15 o C 10 o C 0 o C -20 o C –C … Pixel capacity –V 0 … Breakdown voltage 30 o C 25 o C 20 o C 15 o C 10 o C 0 o C -20 o C Gain, Dark Noise Rate, Cross-talk 30 o C 25 o C 20 o C 15 o C 10 o C 0 o C -20 o C Basic performances are almost OK. Further improvements is still ongoing. Over-voltage

Breakdown voltage (V) Pixel capacitance (pF) Variation of Gain over 800 MPPCs Number of MPPCs Device-by-device variation is less than a few %.  No need for further selection or categorization on massive use ! Just need a small tuning of operation voltages. Variation ~ 0.45 V Variation < 4% 800 MPPCs have been measured MPPCs : Dec All measured MPPCs : Feb … Measured after soldered to flat cable.

Dec/06 Feb/07 with flat cable Over-voltage = V bias – V 0 (V) Variation of Dark Noise over 800 MPPCs Noise Rate (kHz) Noise rate is far less than 1 MHz with all the samples. Device-by-device variation is order of ~10 %.

Photon Detection Efficiency MPPC 0.5 mm  hole PMT LED WLSF ~ 16 % Measured by njecting same light pulse into both MPPC and PMT, and comparing light yield. MPPC PMT The 1600-pixel MPPC has comparable P.D.E. with normal photomultipliers (15~20%).

Recovery Time Measurement MPPC delay LED Inject strong laser (width=52 ps) into the MPPC After delay of  t, inject strong LED light pulse and measure MPPC pulse height. Compare the MPPC output for the LED pulse between with and without the first laser pulse. tt Black … MPPC output for Laser pulse Green … MPPC output for LED pulse Red … Laser + LED Blue … (Laser+LED) - Laser Ratio of Blue / Green shows recovery fraction. t (nsec) Oscilloscope view

Recovery Time Result The curve is fit with a function t D : dead time  : recovery time Delay Recovery fraction (%) V bias (V)  (nsec) t D (nsec) Recovery time of the 1600-pixel MPPC is measured to be 4 ns. Shape does not depend on bias voltage.

Response Curve Response curves taken with various width of LED light pulses Linearity is not limited by number of pixels thanks to quick recovery ! No significant influence from changing bias voltage. Time structure of the light pulse gives large effects in non-linear region. Knowing time structure of input light is important. 8 ns 16 ns 24 ns w = 50 ns 24 ns 8 ns 16 ns 1600 PMT LED w

MPPCs (1600 pixels) The GLD ECAL prototype Scintillator strip (1 x 4.5 x 0.3 cm) Frame WLS fiber Tungsten (3.5 mm thick) Scintillator layer (3 mm thick) e+e+

6 GeV e + center injection GeV Result of beam test with 1-6GeV positrons

Summary We are testing the 1600-pixel MPPC for the GLD calorimeter. Measured performance is almost sufficient for the requirement –Comparable gain / P.D.E. with photomultipliers. –Low noise rate (~100kHz) comparing with SiPMs. Variation of gain and noise rate among 800 samples are small enough (<10%). Dynamic range is enhanced thanks to the short recovery time. The MPPC is feasible for the GLD calorimeter readout.