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Deng Ziyan Jan 10-12, 2006 BESIII Collaboration Meeting
BESIII TOF Simulation Deng Ziyan Jan 10-12, 2006 BESIII Collaboration Meeting
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Outline TOF geometry Geant4 hits recording Digitization based on hits
Light production Light propagation PMT response Discrimination
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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
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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
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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
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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 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 rise time = 0.9 ns
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Simulation of Light Propagation
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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%
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Collection Factors (4) Quantum efficiency of PMT photocathode (5)
Collection factor of PMT dynode: 60% number of generated photoelectrons 20%
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Time Distribution time of photoelectrons
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PMT Response time response function for single photoelectron signal
rise time=2.5ns PMT signal pulse MeanPulseHeight=50mv
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Preamplifier and Discriminator
TDC and ADC MeanPulseHeight=500mv electronic noise added LT TDC rise time:4ns low threshold (LT) = 50mv high threshold (HT)= 250mv
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Time Walk before T-Q correction after T-Q correction
0.8GeV electron, perpendicular incidence
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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
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More to do Add uncertainty from start point
start position start time t0 More research on end-cap TOF digitization
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The end Thanks!
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