Study and Development of the Multi-Pixel Photon Counter for the GLD Calorimeter Satoru Uozumi (Shinshu, Japan) on behalf of the GLD Calorimeter Group Oct-9 ICATPP 2007 Introduction for ILC, GLD and MPPC MPPC performance Calorimeter prototype with full-MPPC readout

The International Linear Collider and GLD Center-of-mass energy at 0.5 ~ 1 TeV. Various precision measurements expected: –e + e - -> H, W, Z, tt, SUSY, etc …  Multi-jet final states. GLD 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 the precise jet-energy measurement.

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 should be read out individually. Therefore the number of channels is huge (~10M for ECAL, ~4M for HCAL). The calorimeter is placed inside 3T magnetic field. The GLD Calorimeter Need small, cheap, magnetic-field tolerant photon sensor while having high performance.

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 GLD calorimeter readout.

What are required to the MPPC ? Gain, Photon Detection Efficiency (P.D.E.) comparable to PMTs. –Gain at least –P.D.E. ~ 20% (capable to distinguish MIP signal). Acceptable dark noise rate (due to thermal electrons) and inter-pixel cross-talk probability. –Dark noise rate < 1 MHz, Cross-talk probability ~ a few per cent. Uniform performance over many pieces. Dynamic range enough to measure ~100 GeV photons. –corresponds to ~5000 photoelectrons. –MPPC is non-linear device.  necessary to know right response curve for correction. Stability & Robustness. Tolerance to temperature change, long-term use, magnetic field and radiation. Low cost, compactness. –Price order of $1~5, package fitting to 2 mm thick scintillator strip. Time resolution ~ 1 ns 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 Basic performances are almost OK. Further improvement is still ongoing. Over-voltage

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. Noise Rate (kHz) Over-voltage (V) kHz 400 kHz Gain – 800 pieces Noise Rate 450 pieces

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 another laser light pulse and measure MPPC pulse height. Compare the MPPC output for the second laser pulse between with and without the first laser pulse. 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 (with x63 amp) tt

Recovery Time Result The curve is fitted with a function : 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). where  indicates the recovery time pixel

Response Curve The MPPC output is non-linear to input because one pixel basically can count only one photon. Correction for the saturation effect is important for precise energy measurement. However the MPPC recovery time is ~ 4 ns, comparable with scintillator light signal. In such a case, one pixel may output signal several times for a single light input from the scintillator. Shape of response curve may change with time structure of light input, due to the quick recovery  check with actual measurement pixel Simulated response (no quick recovery)

Response Curve Response curves measured with various width of LED pulses Linearity of 1600 pixel MPPC 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 1600 PMT LED w

MPPCs (1600 pixels) The GLD ECAL prototype 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+ In 2007 March beam test has been performed at DESY using 1-6 GeV e + beams. World’s first trial to test the scintillator-strip calorimeter with MPPC ! 468 channels In total

e+e+ X Y e+e+ e+e GeV Performance of the EM Calorimeter Prototype Unexpectedly excellent linearity, even without correction for MPPC saturation ! Energy resolution is consistent with expectation. Event display 6 GeV e + Measured energy spectra Energy resolution Linearity + 1%

Summary & Prospects The MPPC is a promising device which has lots of excellent features ! We are developing and studying the MPPC collaborating with Hamamatsu in order to utilize it for the GLD calorimeter readout. 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. –Knowing the time structure of light input is important. 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. –More precise understanding of the MPPC (after-pulse etc …)

Backups

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 !

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

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.