1. Ilhan TAPAN* and Fatma KOCAK
Simulation Work on Calorimetric Energy Resolution for the TAC-PF Detector
Ilhan TAPAN* and Fatma KOCAK
Uludag University
Physics Department
Bursa-Turkey
* on behalf of TAC-PF group
Title: Excess Noise Factor of Neutron Irradiated Silicon Avalanche Photodiodes
The XVth International Conference on Calorimetry in High Energy Physics,
Santa Fe, NM , June 4-8, 2012

2. - Brief Introduction of TAC project
Outline
- Brief Introduction of TAC project
- Crystals- Photodiode Combination
- Calorimetric Energy Resolution
- Calculations and Results
- Conclusion
Motivation: CMS & APDs

3. Turkish Accelerator Center (TAC) Project
The mission of TAC is to design, construct and use high energy particle accelerators for scientific researches in Turkey and in the region and to collaborate with international HEP community.

4. The ongoing project has three main parts
1) Accelerator Based Light Sources, 2) Proton Accelerator (PA)
3) Particle Factory (PF)
An electron-positron collider as a “super charm factory,
1 GeV electron linac and a 3.56 GeV positron ring for linac on ring
type collisions and a dedicated detector.
Produce charm meson resonantly at the center of mass energy
of 3.77 GeV.
Motivation: CMS & APDs

5. TAC super charm factory parameters
e--linac
e+-ring
Energy, GeV
1.00
3.56
Particles per bunch, 1010 2 20
 function at IP, mm
80/5
x/y/z, m/m/mm
36/0.5/5
Beam current (A)
0.48
4.8
Circumference, m
600
Crossing angle, mrad 34
Collision frequency, MHz
150
Luminosity, cm-2s-1
1.41035
Motivation: CMS & APDs

6. Crystals- Photodiode Combination
The energy measurement is based on the energy released of the incident particles in the crystal material.
An electromagnetic shower is produced by a high-energy electron, positron or photon enters the crystal.
The light generated in the shower development is detected by photodetectors.
PbWO4 and CsI(Tl) crystals are considered for the construction of the TAC-PF electromagnetic calorimeter.
Motivation: CMS & APDs
The generated photons in the crystal material are detected by Avalanche photodiodes (APD) or PIN photodiodes placed at the end of the crystal.

7. PbWO4 Crystal Advantages  Disadvantages  Dense and Radiation hard
Short radiation length
Fast
Disadvantages 
Temperature dependence
Low light yield
Properties of PbWO4
Density
8.28 g/cm3
Radiation length
0.89 cm
Interaction length
19.5 cm
Moliére radius
2.2 cm
Emission peak
420 nm
Light yield
120 photons /MeV
Radiation hardness
107 rad
Lcr = 20 cm = 22.5X0
Motivation: CMS & APDs

8. CsI (Tl) Crystal
Lcr = 30 cm = 16.2X0

9. Hamamatsu S-8148 silicon APD
Advantages 
compact and robust
very high QE
internal gain
very good time resolution
insensitive to B
Produced by epitaxial growth on low
resistivite n+-type silicon substrate,
followed by ion implantation.
Disadvantages 
small sensitive areas and noisy
gain fluctuations
dependence on high radiation
Active area; 5x5 mm2

10. Hamamatsu S2744-08 silicon PIN Photodiode
Active area; 1x2 cm2
Photosensitive area: mm x 20mm
Thickness of Wafer: μm
Quantum efficiency(560nm): %
Supplies Reverse Voltage : V
Capacitance : PF
Dark current: nA
Temp. dependence for noise: %/0C

11. Calorimetric Energy Resolution
Energy resolution in the ECAL
E : the energy of the incident particle
a : stochastic term
(photoelectron statistics, shower fluctuations, photo- detector,
lateral leakage)
b : constant term
(non-uniformities, longitudinal leakage)
c : noise term
Introduction: ECAL Energy Resolution

12. Calorimetric Energy Resolution
The total stochastic term of the energy resolution for crystal- photodiode combination is composed of a contribution from shower containment (lateral leakage contribution) and a contribution from photodiode signal fluctuation (photo-electron statistics).
a lateral : Event to event fluctuations in the lateral shower containment
a pe : Photoelectron statistics contribution from photodetector
F is the avalanche gain fluctuation or excess noise factor
Npe is the number of primary photoelectrons
Npe = Nph .QE
Nph ; photons from crystal, QE ; quantum efficiency

13. Calorimetric Energy Resolution
Excess Noise;
Hamamatsu S APD
M : avalanche gain
: avalanche gain fluctuation
The emission weighted excess noise
PbWO CsI(Tl)
Hamamatsu S2744 PD
Hamamatsu S8664 APD
wavelength dependent
excess noise and emission

14. Calorimetric Energy Resolution
Quantum efficiencies are wavelength dependent.
The emission weighted quantum efficiency
wavelength dependent
quantum eff. and emission
PbWO CsI(Tl)
Hamamatsu S2744 PD % %
Hamamatsu S8664 APD % %
Nph : Number of the incident photons collected by the PD
Npe : Number of the primary electrons created in the PD

15. Calculations
The contribution to the calorimetric energy resolution from both the shower fluctuations in the crystal and photoelectron statistics in the detectors have been calculated for PbWO4-APD/PIN and CsI(Tl)-APD /PIN combinations.
The generated light in the crystals and the number of photons collected from photodiodes have been calculated for GeV incident photons using the GEANT4 simulation code.
PbWO4
same size in PANDA EMC;
a length of 20 cm (22.5X0)
cross section 2.2x2.2 cm2
CsI(Tl)
a truncated-pyramidal shape;
a length of 30 cm (16.2X0)
front side 5.5x5.5 cm2
rear side 6x6 cm2
Photodiode
photon

16. Calculations: simulation of alateral
The contribution to the stochastic term coming from fluctuations in the lateral shower containment has been simulated for 3x3 and 5x5 crystal matrices.
CsI(Tl)
central
3x3
5x5
PbWO4
Energy responses to 2 GeV photons observed in the central module and the crystal matrices.

17. Calculations: simulation of alateral
Geant4 results of the shower fluctuation ( ) and the leakage out of the crystal.
3x3 :
5x5 :
3x3 :
5x5 :

18. Calculation of ape
The ape photoelectron statistics contribution on the stochastic term has been calculated from;
1.8% for PbWO4-APD,
0.48% for PbWO4-PIN
and
0.24% for CsI(Tl)-APD,
0.04% for CsI(Tl)-PIN
combinations.
Npe = 5100 pe/MeV
Simulation
Npe = 5000 pe/MeV
NIM A 494 (2002) 298–302

19. Results
“a” term indicates shower fluctuations for 5x5 crystal matrices and photoelectron statistics.
“a” term and a part of the “b” term originate from the shower-leakage fluctuation.

20. Conclusion Simulation shows that;
PbWO4- photodiodes are not in good combination for lower energies.
PbWO4-APD has bigger “a” values then PbWO4-PIN combination.
Best choice is CsI(Tl)-PIN combination

21. Additional slides For the 3x3 matrix
IEEE TRANS. on NUCL. SCI, VOL. 55, NO. 3, 2008, p 1298
For the 3x3 matrix
NIM A 479 (2002) 117–232

22. Calorimetric Energy Resolution and Stochastic Term
APD contributes to all the terms ECAL energy resolution
a sensitive area, quantum efficiency, excess noise
b gain sensitivity to operating voltage and temperature,
aging and radiation damage
c low capacitance, serial resistance and dark current
By neglecting the intrinsic resolution, the APD photo-electron
statistics contribution to stochastic term is given by
Introduction: ECAL Energy Resolution
Npe is the number of primary photoelectrons
Npe = Nph .QE
Nph ; photons from crystal, QE ; quantum efficiency
F is the avalanche gain fluctuation or excess noise factor

23. Calorimetric Energy Resolution and Stochastic Term
The relative fluctuation of the APD signal in the proportional mode
Npe is the number of primary photoelectrons
: S.D. of the number of primary photoelectrons;
M : Avalanche gain
σM : S.D. of the avalanche gain
APD photo-electron statistics
contribution to stochastic term

24. Energy deposition in the crystals- 2 GeV