Study of the Multi-Pixel Photon Counter for ILC calorimeter Satoru Uozumi (Kobe University) Atami Introduction of ILC and MPPC The MPPC performance Calorimeter Prototype with MPPC Summary

The International Linear Collider and ILD E TOT = p e + p  + p charged hadron + E  + E neutral hadron [ tracks only] [calorimeter only] Separation of jet particles in the calorimeter is required for the PFA  Fine granular calorimeter is necessary. Particle Flow Algorithm (PFA) allows precise jet-energy measurement. e + e - collider with center-of-mass energy at 500 ~ 1000 GeV. ILD (International Large Detector) is one of the detector concepts proposed for the ILC experiment. Various precision measurements expected: –e + e -  H, W, Z, tt, SUSY, etc …  Multi-jets final states.

One approach for the fine granular calorimeter. other approaches : silicon strip cal, digital cal Sampling calorimeter with W/Pb - scintillator sandwich structure. Scintillator stirp structure to achieve fine granularity (strip size ~ 1 x 4.5 x 0.2~0.3 cm). Signal of all the strips are read out individually.. Therefore the number of channels is huge (~10M for ECAL, ~4M for HCAL). The calorimeter is placed inside 3 T magnetic field. The ILC Scintillator-Strip Calorimeter Need small, cheap, magnetic-field tolerant photon sensor while having high performance comparable with conventinal PMTs.

Belongs to Pixelated Photon Detector family (same as SiPM) Manufactured by Hamamatsu Photonics. High Gain (10 5 ~10 6 ) Good Photon Detection Efficiency (~15% with 1600 pixel) Compact (package size ~ a few mm) Low Cost Insensitive to magnetic field Dark noise exists ( ~100 kHz) Input vs output is non-linear ~ 1 mm Substrate The Multi-Pixel Photon Counter (MPPC) - A Geiger-mode avalanche photo-diode with multi-pixel structure - We are developing and studying the 1600-pixel MPPC with Hamamatsu for the ILD calorimeter readout.

What are required to the MPPC ? Gain, Photon Detection Efficiency (P.D.E.) comparable to PMTs. –Gain at least 10 5 –P.D.E. ~ 20% Dark noise rate (due to thermal electrons) and inter-pixel cross-talk probability as low as possible. –Dark noise rate < 1 MHz, Cross-talk probability ~ a few per cent. Uniform performance over many pieces. Dynamic range enough to measure EM shower max. –Electromagnetic shower is quite dense. –Need dynamic range corresponds to 2000~5000 photoelectrons. Stability & Robustness. Tolerance to temperature change, long-term use, magnetic field and radiation. Low cost, compactness. –Price order of $1~5, package size ~ 2 x 2 mm 2. Time resolution ~ 1 ns –Useful for bunch-ID, neutron separation

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, Inter-pixel Cross-talk 30 o C 25 o C 20 o C 15 o C 10 o C 0 o C -20 o C Gain comparable to conventional PMTs. Dark noise rate ~100 kHz. Performance is temperature sensitive.  temperature control / monitoring is important. Over-voltage 1600 pixel  V 0 /  T = (56.0±0.1) mV/ o C

Piece-by-piece Variation Piece-by-piece variation is acceptably small.  No need for further selection or categorization on massive use ! Just a small tuning of operation voltages is necessary. Further effort is ongoing by Hamamatsu to make the variation even smaller. Noise Rate (kHz) Over-voltage (V) kHz 400 kHz Gain – 800 pieces Noise Rate 450 pieces

Photon Detection Efficiency (PDE) 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%) pixel

Response Curve If the recovery time is very long, MPPC output is defined only by number of pixels. However if the recovery time is shorter than input light, dynamic range may be enhanced. Linearity of 1600 pixel MPPC is not limited by number of pixels thanks to quick recovery time (~4ns). 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 1600 PMT LED w MPPC 1600pix Simulation Slow recovery pix Results

Performancestatus Gain10 5 ~10 6 OK Photon Detection Eff.~0.2 for 1600 pix. MPPCOK Dark Noise Rate~ 100 kHzOK Photon countingGreatOK Bias voltage~ 70 VOK SizeCompactOK Dynamic range Determined by # of pixels and recovery time underway CostExpected to be < $10Negotiating Long-term StabilityUnknown To be checked RobustnessUnknown, presumably goodunderway Radiation hardnessConcernedunderway B fieldExpected to be Insensitive Looks OK Timing resolutionExpected to be 0.1~1 ns To be checked Things done / not yet done

ECAL Prototype Performance MPPCs (1600 pixels) Scintillator strip (1 x 4.5 x 0.3 cm) Frame WLS fibre Tungsten (3.5 mm thick) Scintillator layer (3 mm thick) e+e+ 468 channels In total (1-6 GeV) Linearity + 1% Energy Resolution for e + The calorimeter with Full MPPC readout is proven to work !

Summary & Prospects For the ILC calorimeter readout, study of the MPPC is extensively ongoing collaborating with Hamamatsu. Measured performance of 1600 pixel MPPC is almost satisfactory for the requirement: –Comparable gain / P.D.E. with photomultipliers. –Low noise rate (~100kHz) comparing with SiPMs. –Small piece-by-piece variation. –Short recovery time enhances the dynamic range for scintillator signal. The first EM calorimeter prototype with MPPC readout shows good and reasonable performance. We are still working on further study and improvement. –More number of pixels for more dynamic range. –Need to check long-term stability, robustness, radiation hardness. The MPPC is a promising device which has lots of excellent features !

Number of pixels Sensor size1 x 1 mm 2 Nominal Bias Volt V77 10 V Gain (x 10 5 ) Noise Rate (kHz) Photon Detection Efficiency65 %50 %25 % Temperature dependence (  V 0 /  T) 50 mV / o C The MPPC Line-up Comparing with other Pixelated Photon Detectors (PPD), the MPPC has, Low dark noise High sensitivity to blue light Small device-by-device variation From HPK catalog

MPPC New Release Timeline (informed at NSS Nov 2007 by Hamamatsu) 2007 Dec : 3x3 mm 2 commercial sample 1x1mm 2 SMD small package mechanical sample 2x2, 1x4 Array (3x3mm 2 ) mechanical sample 2008 Jan : SMD small package commercial samples 2008 Apr : 3x3 mm 2 product release Array commercial samples 1x4 array 2x2 array

Backups

Recovery Time Measurement 1600 pixel t (nsec) Oscilloscope view (with x63 amp) tt Black … MPPC output for 1st Laser Green … MPPC output for 2nd Laser Red … Laser + LED Blue … (Laser+LED) – Laser = net response to 2 nd laser Ratio of Blue / Green gives recovery fraction. Recovery time of the 1600-pixel MPPC is measured to be ~ 4 ns. This number is consistent with RC time constant of a pixel (C ~ 20 fC, R ~ 200 k , RC ~ 4 ns).

Excellent photon counting ability 0,1,2,3,4,5,6,7,... Photoelectrons ! 1 photoelectron 2 photoelectrons

PhotomultiplierMPPC Gain~ ~10 6 Photon Detection Eff.0.1 ~ 0.2~0.2 for 1600 pix. MPPC Responsefast Photon countingYesGreat Bias voltage~ 1000 V~ 70 V SizeSmallCompact B fieldSensitiveInsensitive CostVery expensive !Not very expensive Dynamic rangeGoodDetermined by # of pixels Long-term StabilityGoodUnknown Robustnessdecent Unknown, presumably good Noise (fake signal by thermions) QuietNoisy (order of 100 kHz) The MPPC has lots of advantages The MPPC is a promising photon sensor, and feasible for the GLD Calorimeter readout !

Radiation hardness of MPPC (100 / 400 pixels) Gamma-ray Neutron 3.3 x 10 7 n /cm1 x n /cm Proton irradiation (400 pixel MPPC) 100 pixel MPPC