Application of novel Silicon-based photo-detectors to calorimetry and medical physics

1. tracker calorimeter Application of novel Silicon-based photo-detectors to calorimetry and medical physics MPPC Nicola D’Ascenzo, Erika Garutti, Martin Göttlich University of Hamburg – DESY Hans-Christian Schultz-Coulon, Alexander Tadday University of Heidelberg

2. 1x1 mm2 active area 3x3 mm2 active area The Multi Pixels Photon Counter(from Hamamatsu) The MPPC is a multi-pixel avalanche photo-diode operated in Geiger mode calorimetry application Blue sensitive device: ideal for direct r/o of plastic scint. and crystals PET application Erika Garutti - IEEE

3. MPPC characterization intrinsic recovery time of MPPC ~ 4 ns measured at university ofShinshu (see talk S. Uozumi, N41-4) response curve to a 50ns long light signal dynamic range artificially extended for long signals due to fast recovery time MPPC 1600pix has ~ 6000 effective pix. for 50ns long signal Erika Garutti - IEEE

4. Application in HEP calorimeters Task: readout of active layers of highly-segmented and granular calorimeter Single calorimeter cell readout with SiPM 3x3 cm2 x 0.5 cm thick see talk by F. Sefkow, N13-5 CALICE test beam CERN 2007 DATA prototype active layer 100x100 cm2 • Requirements to photo-detector: • insensitive to B-field (~ 5T) • couple to organic scintillator (green/blue) • low noise (dark rate + cross talk above thresh.) ~ 10-4 • detection eff. for Minimum Ionizing Particles* >95% •  light yield for MIP ~10 pixels • dynamic range ~ 100-500 MIP ~8000 SiPM operated Erika Garutti - IEEE * one MIP in 0.5 cm scintillator ~ 10000 g ( · WLS eff ~ 200 g on SiPM)

5. Present status SiPM 1056 pixels (MEPHI/Pulsar, RU) green sensitive Scintillator tile (Uniplast, Vladimir RU) + Green wavelength shifter fiber (Kurakay) Readout of plastic scintillators with MPPC study driven by calorimetry applications for a ILC detector MIP response to Ru106 source 3 cm MPPC 1600 px operation point w WLS fiber light yield [pixels/MIP] R&D: direct r/o of scintillator tiles 3x3x0.5cm3 direct r/o Vbias - Vbreakdown [V] MPPC directly coupled  LY sufficient for calorimeter application but higher LY would allow thinner tiles (lower cost) Erika Garutti - IEEE

6. Readout of plastic scintillators with MPPC MIP collection efficiency noise spectrum w WLS fiber threshold at 1.5 pix dark rate < 3 kHz direct r/o • ILC requirement • dark rate < 300 Hz • MIP eff ~ 95% low but acceptable MIP detection efficiency > 97% for all r/o combinations comparable with present status 400 px Cut at3KHz MIP spectrum  larger dynamic range than at present 1600 px Erika Garutti - IEEE

7. Application in PET detectors reduction of background Task: identify back-to-back scattered 511 keV photons from e+e- annihilation suppress background and determine true line of response Background events remove combinatorial bg by ToF meas. Dt = 500 ps  remove Compton-scattered g with good energy resolution Erika Garutti - IEEE

8. 2 x scintillator crystals LSO*: 1x1x15 mm3 3x3x15 mm3 LFS**: 3x3x15 mm3 emission: ~420 nm decay time: ~40 ns Teflon wrapping 2 x MPPC 1x1 mm2, 400 pixels 3x3 mm2, 3600 pixels coupled with optical grease Na22 source Readout of scintillators crystals with MPPC study driven by possible PET applications • due to high MPPT gain (7.5x105) no amplification needed  simple readout • energy integral on VME QDC (Lecroy 1182) • time resolution measurement: 4 GHz Oscilloscope, 50 ps resolution (Textronix TDS7404B) * Lutetium OrthoSilicate from Heilger Crystals ** Lutetium Fine Silicate from Lebedev, Moskow Erika Garutti - IEEE

9. Readout of scintillators crystals with MPPC Energy resolution 3x3 mm2 systems 1x1 mm2 system LSO Crystal MPPC 400 MPPC 3600 blue sensitivity ~ 8% for LSO negligible • LSO and LFS similar performance (within syst. uncertainty of ~ ± 2%) • Result comparable with typical value for LSO crystals + PMT is DE/E ~ 10 % @ 511 keV Erika Garutti - IEEE ! after 4 months of test E resolution ~ 13±2%  degradation of MPPC package or crystal surface ?

10. Issue of MPPC saturation 3600 pix. MPPC coupled to 3x3x15 mm3 LSO crystal QDC spectrum scope signal • integral of 511 keV g signal ~ 2000 p.e. • ! but: signal width ~120 ns • peak amplitude ~ 400 p.e. • below saturation estimated at > 10000 pix. for 3600 pix. MPPC and 120 ns signal • but MPPC response non-linear everywhere (see talk N18-2, K.C. Burr) Erika Garutti - IEEE

11. Npe 1. Readout of scintillators crystals with MPPC Time resolution • Procedure for time resolution measurement: • 0. store two waveforms from scope if amplitude > noise level (~ 2mV or ~10 pixels) • apply energy cut to exclude Compton background • define a timing threshold to measure time difference between signals 2. tcut two waveforms from the photon peak the voltage of the two MPPC is tuned to give same response to 511 keV g Erika Garutti - IEEE

12. # events 2 photon-peak amplitudes Compton background Background time difference [ns] Time resolution: result fix threshold discr. threshold [pixels] • Npe = ± 1 s of photon peak • ~10-15% of collected events used • for lowest threshold FWHM ~ 650 ps limited by scope noise *no Jitter analysis package used for this analysis Photoelectric Constant fraction discr. Erika Garutti - IEEE

13. Conclusions • MPPC 400 and 1600pix very good candidates for highly-granular calorimeter: - direct coupling to plastic scintillator - LYMIP ~ 7 (10) p.e. with direct coupling (WLS fiber mediated coupling) - satisfactory MIP detection efficiency with required noise cut • MPPC 3600 pixels excellent performance for PET application: - E resolution comparable to PMT - t resolution < 650 ps (noise limited) • next step: build 2 matrices of 6x6 MPPC with individual readout to test homogeneity, stability, reproducibility, calibration, multi-channel system 6x6 LFS crystals 3x3x15 cm3 6x6 MPPC 3600 we would like to thank Hamamatsu for providing the MPPC samples for this study Erika Garutti - IEEE