1. 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
calorimeter
tracker

2. The Multi Pixels Photon Counter (from Hamamatsu)
The MPPC is a multi-pixel avalanche photo-diode operated in Geiger mode
# Pixels (size mm2)
Pieces
Bias
Dark Rate
>0.5pixels
> 1.5 pixels
Gain
(10^5)
400 (1x1) 5
76 V
kHz
9-10 kHz
1600 (1x1)
78 V
kHz
kHz
3600 (3x3)
70 V
MHz
kHz
calorimetry
application
1x1 mm2 active area
Blue sensitive device:
ideal for direct r/o of plastic scint. and crystals
PET application
3x3 mm2 active area
1 Nov. 2007
Erika Garutti - IEEE

3. MPPC characterization
intrinsic recovery time
of MPPC ~ 4 ns
measured at university of Shinshu (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
1 Nov. 2007
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 ~ MIP
~8000 SiPM
operated
1 Nov. 2007
Erika Garutti - IEEE
* one MIP in 0.5 cm scintillator ~ g ( · WLS eff ~ 200 g on SiPM)

5. Readout of plastic scintillators with MPPC
study driven by calorimetry applications for a ILC detector
MIP
Scintillator tile (Uniplast, Vladimir RU) + Green wavelength shifter fiber (Kurakay)
Present status
SiPM 1056 pixels
(MEPHI/Pulsar, RU)
green sensitive
response to
Ru106 source
3 cm
MPPC 1600 px
operation point
light yield [pixels/MIP]
w WLS fiber
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 at 3 KHz
MIP spectrum
 larger dynamic
range than at present
1600 px
1 Nov. 2007
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 Compton-scattered g
with good energy resolution
remove combinatorial bg by ToF meas.
Dt = 500 ps 
1 Nov. 2007
Erika Garutti - IEEE

8. Readout of scintillators crystals with MPPC
study driven by possible PET applications
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
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
1 Nov. 2007
Erika Garutti - IEEE

9. Readout of scintillators crystals with MPPC
Energy resolution
1x1 mm2 system
3x3 mm2 systems
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 ~ keV
! after 4 months of test E resolution ~ 13±2%  degradation of MPPC package or crystal surface ?
1 Nov. 2007
Erika Garutti - IEEE

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 > pix. for 3600 pix. MPPC and 120 ns signal
but MPPC response non-linear everywhere (see talk N18-2, K.C. Burr)
1 Nov. 2007
Erika Garutti - IEEE

11. 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
Npe 1. 2.
tcut
two waveforms from the photon peak
the voltage of the two MPPC is tuned
to give same response to 511 keV g
1 Nov. 2007
Erika Garutti - IEEE

12. Time resolution: result
Background
# events
time difference [ns]
2 photon-peak amplitudes
Compton background
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.
1 Nov. 2007
Erika Garutti - IEEE

13. Conclusions we would like to thank Hamamatsu
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
1 Nov. 2007
Erika Garutti - IEEE