1. KM2A Electron Detector Optimization
Jing Zhao
THE 2nd WORKSHOP OF AIR SHOWER DETECTION AT HIGH ALTITUDES

2. outline Optimization intention Design and implemention in GEANT4
Comparison with experiment and simulation

3. Optimization intention
KM2A array for γdetection >50TeV, it needs 5137 EDs.
For one ED:
Measurement range of charged particles:1－4000，
Resolution: particles
>15p.e. in case of 1 particle(for the electronic need)
A GEANT4-based simulation package have been developed in the main purposes as below,
To confirm the performances of “tile”, ED’s prototype, used in the engineering array now
To optimize the new design of ED

4. ED prototypes used in Engineering array and their performances
Scintillation detectors, called “cassette”, were chosen to apply for the engineering array, while here PHOTONIS XP2012B PMTs were used in light detection.
“cassette”
Fig. One prototype of ED , scintillation detector, called “cassette”
clear fibers
WLS fibers
16 tiles (4×4 tiles) consist of one “cassette”, which efficient detection area is 1.0 m2.
在此处介绍prototype
“Tile”
Fig. two scintillation units (called “tile”, 25cm×25cm×2cm each)

5. Design and implementation in Geant4
Optical process
Optical Photon Production
Cerenkov Process
Scintillation Process
Transition Radiation
Processes affecting Optical Photons
Refraction and Reflection
Bulk Absorption
Rayleigh Scattering
Class Categories (experimental setup)

6. Implementation in Geant4
Input scintillator emission spectrum
Implementation in Geant4
Geometry Implementations
1. Scintillator :
Size : 25x5cm -> 25x25cm
Materal: Polystyrene
Yield: 8000/MeV
n = 1.60
2. Wavelength shift plastics/optical fiber
d = 1.50 mm (tclad = 0.03d)
n = 1.60, core
1.49, cladding layer
Need input parameters for WLS plastics.
like absorption length,emission spectrum
Surface condition( Ground)
for total internal reflection.
WLS fiber absorption length
WLS fiber absorption and emission spectrum
concrete

7. Experiment 1:Direct readout
Cosmic- telescope 4 1 2 3
5cm
13cm
1cm
trigger
PMT
scintilllator
The scintillator size: 25x25x2cm3

8. Comparison result 1 :direct readout4 1 2 3
5cm
13cm
1cm

9. Experiment 2:Fiber readout
trigger
PMT
scintillator
test1
test2
25x25x1cm3+5fiber
(kedi)
25x5x1cm3+1fiber
25x25x2cm3+8fiber
(UPS89)

10. Comparison result 2:fiber readout
Fiber readout test1
Scintillator Size
Fiber num
Tyvek
Npe of
exp
sim
Sim/exp
25x25x2 8 no 5
31.86
6.37
yes 10
74.1
7.41 2
2.33
Fiber readout test2
Scintillator Size
Fiber num
Tyvek
Npe of exp
Npe of sim
Sim/exp
25x5x1 1
yes
6.4
68.2
10.66
25x25x1 5 8
82.8
9.52
1.25
1.21

11. Check the photons transmission
To understand the above big differences between the simulation results and the experimental ones , two estimations were done as follows:
It seems there was no problem in the tracking processes of our package.
The big differences indicate that the present description of the coupling between fibers and scintillators is too ideal to simulate the roughness of the surfaces of those grooves or holes properly.
In addition, some parameters, such as fiber absorption length, should be considered in further step.
But the about disscussion would not affect the application of present simulation package for optimization of ED design because the simulation results are consistent with the experimental ones in proportion.
2.In veiw of the isotropy of re-emitted photons in the WLS fiber, the ratio between the trapped photos (due to the total internal reflection) and all re-emitted ones is 12%, which is consistent with the simulation values.
1.The ratio between the number of photons passing through the fibers and the number of photons generated in the scintillator is about 6.1%, while the acceptance is 6% in view of the solid angle of the fibers in scincillator.

12. optimization of the tile size and fiber number
Blue:8 fbier red:5fiber
Scintillator Size
Fiber num
Tyvek
Npe of exp
25x5x1 1
yes
6.4
25x25x1 5 8
1.25
Using 25x25x1cm3+5fiber(kedi) scintillator as 1

13. summary A GEANT4-based simulation package has been developed.
Results are consistent with the ones of direct readout experiment.
On the optimization of ED prototype with Fiber readout, there are big differences on light collection betweent the simulation results and the experimental ones.These simulation studies continue.