1. Deng Ziyan Jan 10-12, 2006 BESIII Collaboration Meeting
BESIII TOF Simulation
Deng Ziyan
Jan 10-12, 2006
BESIII Collaboration Meeting

2. Outline TOF geometry Geant4 hits recording Digitization based on hits
Light production
Light propagation
PMT response
Discrimination

3. TOF Geometry Dimensions and materials same as designed
Scintillator (EJ200)
Wrapping materials (Al + PVF)
PMT (R5924)
Barrel TOF
End-cap TOF
EMC
barrel
end-cap

4. Geant4 Hits Geant4 hits recorded at discrete steps along track
Global time, step time, position, direction
scintillator ID, energy loss…
hit
0.8 GeV/c electron perpendicular incidence

5. Digitization based on hits
Geant4
Get hit information: energy loss, time, position
Scintillator
Scintillator light emission
Light propagation
PMT
Photoelectrons production
Signal pulse generation
Discriminator
output TDC and ADC
Digitization

6. Characteristic Parameters
Scintillator (EJ200)
Scintillation Efficiency
8000 photons/MeV
Rise Time
0.9 ns
Decay Time
2.1 ns
No. Atoms H:C
11:10
Refractive Index
1.58
Bulk Attenuation Length
3.8 m
Density
1.032 g/cm3
PMT (R5924)
Photocathode Diameter
39 mm
Spectral Range nm
Rise Time
2.5 ns
Transit Time
9.5 ns
Transit Time Spread
0.44 ns
Collection factor
0.6
Gain at 1 tesla
2.5 x 105

7. Simulation of Light Emission
Light uniformly emitted along step
Isotropic angular distribution
Number of photons proportional to energy loss
Emission time
rise time = 0.9 ns

8. Simulation of Light Propagation

9. Collection Factors (1) Light atttenuation in scintillator
(3) Response of incident angle
at PMT front glass
(2) Mismatch between
scintillator and PMT
Average: 66%
40%

10. Collection Factors (4) Quantum efficiency of PMT photocathode (5)
Collection factor of PMT dynode: 60%
number of generated photoelectrons
20%

11. Time Distribution
time of photoelectrons

12. PMT Response time response function for single photoelectron signal
rise time=2.5ns
PMT signal pulse
MeanPulseHeight=50mv

13. Preamplifier and Discriminator
TDC and ADC
MeanPulseHeight=500mv
electronic noise added LT
TDC
rise time:4ns
low threshold (LT) = 50mv
high threshold (HT)= 250mv

14. Time Walk before T-Q correction after T-Q correction
0.8GeV electron, perpendicular incidence

15. beam test result Effective speed Veff = 17.7 cm/ns
Intrinsic time resolution at z=0 : 85 ps
beam test result
Effective attenuation length λ= 318cm

16. More to do Add uncertainty from start point
start position
start time t0
More research on end-cap TOF digitization

17. The end
Thanks!