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Geant 4 simulation of the DEPFET beam test
Daniel Scheirich,
Peter Kodyš,
Zdeněk Doležal,
Pavel Řezníček
Faculty of Mathematics and Physics
Charles University, Prague
2-12-2005, Prague
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Index
• Geant 4 simulation program• Model validation• Geometry of the beam test • Unscattered particles• Electron beam simulation
– Residual plots for 2 different geometries– Residual plots for 3 different window thickness
• CERN 180 GeV pion beam simulation• Conclusions
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Geant 4 simulation program• More about Geant 4 framework at www.cern.ch/geant4• C++ object oriented architecture • Parameters are loaded from files
G4 simulation program
class TDetectorConstruction
classTPrimaryGeneratorAction
classTGeometry
classTGeometry
…
classTDetector
classTDetector
…
classTDetector
geometry.configdet. position,det. geometry filessensitive wafers
detGeo1.config
detGeo2.config
…
g4run.mac
g4run.config
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Model validation• Simulation of an electron scattering in the 300m
silicon wafer
• Angular distribution histogram
• Comparison with a theoretical shape of the distribution. According to the Particle Physics Review it is approximately Gaussian with a width given by the formula:
where p, and z are the momentum, velocity and charge number, and x/X0 is the thickness in radiation length. Accuracy of 0 is 11% or better.
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Silicon wafer
electrons
Example of an electron scattering
Angular distribution
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Non-gaussiantails
Gaussian fit
Theoretical shape
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Results: simulation vs. theory
0… width of the theoretical
Gaussian distribution
…width of the fitted
Gaussian
accuracy of 0 parametrisation (theory) is 11% or better
0… width of the theoretical
Gaussian distribution
…width of the fitted
Gaussian
accuracy of 0 parametrisation (theory) is 11% or better
Good agreement between the G4 simulation and the theory
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Geometry of the beam test
Electron beam: 3x3 mm2, homogenous, parallel with x-axis
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(DEPFET)
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Geometry of the beam test: example9
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Geometry 1
Module windows: • 50 m copper foils
• no foils
• 150 m copper foils
Geometry 2
Module windows: • 50 m copper foils
Configurations used for the simulationas planned for January 2006 TB – info from Lars Reuen, October 2005
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Unscattered particle
• Intersects of an unscattered particle lies on a straight line.
• A resolution of telescopes is approximately
pitch/(S/N) ~ 2 m.
• Positions of intersects in telescopes plane were blurred with a Gaussian to simulate telescope resolution.
• These points were fitted by a straight line.
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Residual R(y) in DUT plane
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=0.9912 m =0.9912 m
=0.9928 m =0.9928 m
=0.9918 m =0.9918 m
=0.9852 m =0.9852 m
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Unscattered particles: residual plots
= 1.19 m = 1.60 m = 1.60 m = 1.18 m = 0.99 m
Geometry 1
Geometry 2
= 1.05 m = 1.68 m = 1.68 m = 1.05 m = 0.99 m
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Electron beam simulation
• There are 2 main contributions to the residual plots RMS:– Multiple scattering– Telescope resolution
• Simulation was done for 1 GeV to 5 GeV electrons, 50000 events for each run
• Particles that didn’t hit the both scintillators were excluded from the analysis
2 cuts were applied to exclude bad fits
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Example of 2 cuts
30% of events, 2 < 0.0005
50% of events, 2 < 0.0013
70% of events, 2 < 0.0025
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DUT plane
DUT residual
Actual position
Telescope resolution: Gaussian with = 2 mTelescope resolution: Gaussian with = 2 m
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Electron beam simulation: residual plots19
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Electron beam simulation: residual plots20
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Residual-plot sigma vs. particle energy 21
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Residual plots: two geometriesIdeal detectors
telescopes resolution included
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Residual plots: two geometriesIdeal detectors
telescopes resolution included
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Three windows thicknesses for the geometry 1
Geometry 1
Module windows: • no foils
• 50 m copper foils
• 150 m copper foils
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Residual plots: three thicknessesIdeal detectors
TEL & DUT resolution included
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Residual plots: three thicknessesIdeal detectors
TEL & DUT resolution included
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Pion beam simulation
• CERN 180 GeV pion beam was simulated
• Geometries 1 and 2 were tested
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Ideal detectors
TEL & DUT resolution included
Pion beam: residual plots28
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Ideal detectors
TEL & DUT resolution included
Pion beam: residual plots29
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Conclusions
• Software for a simulation and data analysis has been created. Now it’s not a problem to run it all again with different parameters.
• There is no significant difference between the geometry 1 and 2 for unscattered particles.
• We can improve the resolution by excluding bad fits.
• Geometry 2 gives wider residual plots due to amultiple scattering. For 5 GeV electrons and 30% 2 cut = 4.28 m for the Geometry 1 and = 5.94 m for the Geometry 2.
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Conclusions
• For 5 GeV electrons and 30% 2 cut there is approximately 1m difference between simulations with no module windows and 50 m copper windows.
• CERN 180 GeV pion beam has a significantly lower multiple scattering. The main contribution to its residual plot width come from the telescopes intrinsic resolution.
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