Shower energy systematics in hdgeant/4

Richard Jones, University of Connecticut

January 2, 2018

Purpose

• Claims are made that 2𝛾 mass spectra in the calorimeters are different in hdgeant4 simulations than they are with hdgeant.
• May be due to inconsistent energy scales in the two simulations.
• May originate in either fcal, bcal or both

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1. Compare reconstructed shower energy with generated.
2. Same conditions (control.in) in hdgeant and hdgeant4 sims.
3. Single-photon simulation -- gets rid of position resolution, track matching efficiency, other possible reasons for bias in a 2𝛾 mass spectrum.
4. Separate BCal and FCal showers, check for systematics with polar angle.

Plan:

Part 1: FCal showers

• uniformly generated in energy [0, 2] GeV
• uniformly generated in polar angle [0, 20°], azimuthal angle [0, 360°]
• sliced into bins in polar angle generated
• plot and fit reconstructed shower energy vs generated.
• standard control.in physics settings
• all photons shot from center of target (0, 0, 65) cm
• material interactions (ie. conversions) allowed to happen
• run number 51000 (with magnetic field, no DIRC radiators)
• 100,000 photons generated, 92% are reconstructed as single shower
• only first reconstructed shower is included in plots
• quantity plotted is average reconstructed shower energy

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Fcal: 3° - 5°

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Fcal: 5° - 7°

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Fcal: 7° - 9°

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Fcal: 9° - 11°

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Fcal: 11° - 13°

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Part 2: BCal showers

• uniformly generated in energy [0.5, 1.5] GeV
• uniformly generated in polar angle [22°, 67°], azimuthal angle [0, 360°]
• sliced into bins in polar angle generated
• plot and fit reconstructed shower energy vs generated.
• standard control.in physics settings
• all photons shot from center of target (0, 0, 65) cm
• material interactions (ie. conversions) allowed to happen
• run number 51000 (with magnetic field, no DIRC radiators)
• 100,000 photons generated, ~90% are reconstructed as single shower
• only first reconstructed shower is included in plots
• quantity plotted is average reconstructed shower energy

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BCal: 20°-25°

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BCal: 25°-30°

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BCal: 30°-35°

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BCal: 35°-40°

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BCal: 40°-45°

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BCal: 45°-50°

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BCal: 50°-55°

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BCal: 55°-60°

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BCal: 60°-65°

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BCal: 65°-70°

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Conclusions

1. significant systematic bias is seen as a function of polar angle
2. bias visible both in the fcal and the bcal
3. agreement between hdgeant and hdgeant4 is quite good:
1. very good in the Fcal
2. difference in the Bcal in the y-offset of the E-calibration
4. source of difference in the Bcal not clear -- what would produce an offset?
5. in all cases, size of E-systematic is greater than the hdgeant/4 difference.

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Nonlinear effects

• Next I repeat all of the plots shown above with quadratic fits
• Provides comparison in nonlinear response between hdgeant and hdgeant4
• The data are all the same as shown before, only the fit is different

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Fcal: 3° - 5°

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Fcal: 5° - 7°

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Fcal: 7° - 9°

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Fcal: 9° - 11°

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Fcal: 11° - 13°

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Bcal: 20° - 25°

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Bcal: 25° - 30°

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Bcal: 30° - 35°

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Bcal: 35° - 40°

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Bcal: 40° - 45°

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Bcal: 45° - 50°

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Bcal: 50° - 55°

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Bcal: 55° - 60°

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Bcal: 60° - 65°

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Bcal: 65° - 70°

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Conclusions regarding nonlinear response

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• good consistency between hdgeant and hdgeant4 in both fcal and bcal.
• no residual nonlinearity is observed in the bcal, at least at angles < 70°
• very little residual nonlinearity is observed in the fcal
• quadratic coefficient probably rises to +0.01 around 9°
• then it dives to negative values above 11°, as showers leak out the sides of the fcal
• this latter effect is better treated as an energy leakage than a “nonlinear effect”
• the fcal energy scale still needs work as a polar angle dependent correction
• proposal -- should be applied to the block energies in mcsmear as f(r)

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