Download - BESIII TOF Simulation
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BESIII TOF Simulation
Deng Ziyan
Jan 10-12, 2006BESIII Collaboration Meeting
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Outline
• TOF geometry
• Geant4 hits recording
• Digitization based on hitsLight productionLight propagationPMT responseDiscrimination
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TOF Geometry
barrel end-cap
Dimensions and materials same as designed
Scintillator (EJ200)
Wrapping materials (Al + PVF)
PMT (R5924)
Barrel TOF
End-cap TOF
EMC
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Geant4 Hits
0.8 GeV/c electron perpendicular incidence
Geant4 hits recorded at discrete steps along track
Global time, step time, position, direction
scintillator ID, energy loss…hit
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Digitization based on hits
Geant4Get hit information: energy loss, time, position
ScintillatorScintillator light emissionLight propagation
PMTPhotoelectrons productionSignal pulse generation
Discriminatoroutput TDC and ADCDigitization
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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 300-650 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
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Simulation of Light Emission• Light uniformly emitted along step
• Isotropic angular distribution
• Number of photons proportional to energy loss
• Emission time
2 1
3
/ //
2 1 3
1( ) ( )
1
emit emit
emit
t tt
emit
e e RE t e
R
rise time = 0.9 ns
1
2
3
0.9
2.1
14.2
0.27
ns
ns
ns
R
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Simulation of Light Propagation
90 ,trap trap endless reflection
1
int
0 , sin ( ),airtrap trap
sc
n
nreach PMT
int int int/ cos , / , /pro sc sc pro pro scL d v c n t L v
90 ,trap escape
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Collection Factors
/( ) , 3.8pro proL
pro proR l e m
40%
(1) Light atttenuation in scintillator
(2) Mismatch between scintillator and PMT
(3) Response of incident angle at PMT front glass
cosangle iR
Average: 66%
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Collection Factors(4) Quantum efficiency of
PMT photocathode
20%
number of generated photoelectrons
Collection factor of PMT dynode: 60%
(5)
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Time Distributionpe flight deltaT emit pro TTt t t t t t
deltaTtemitt prot
TTt pet
time of photoelectrons
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PMT Response
2 2
2 2
2 /
2 /( )
4.3
t
e t
t ev t GC
t e dt
ns
time response function for single photoelectron signal
1
( ) ( )pen
PMT ii
V t v t
PMT signal pulse
rise time=2.5ns
MeanPulseHeight=50mv
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Preamplifier and Discriminator
electronic noise added
( )V t dtADC
R
LT
TDC
rise time:4ns
Preamplifier:
low threshold (LT) = 50mvhigh threshold (HT)= 250mv
TDC and ADC( ) ( ), 10PMTV t A V t A
MeanPulseHeight=500mv
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Time Walk
before T-Q correction
after T-Q correction
/T a b Q
0.8GeV electron, perpendicular incidence
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Effective speed Veff = 17.7 cm/ns
Effective attenuation length λ= 318cm
Intrinsic time resolution at z=0 : 85 ps
beam test result
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More to do
• Add uncertainty from start pointstart positionstart time t0
• More research on end-cap TOF digitization
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The end
Thanks!