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Delving Deeper into Geant4

Delving Deeper into Geant4. Guilherme Lima DHCal Meeting October 22, 2003. Updates since last report. Studied the spikes on the distributions of energy depositions in ECal and HCal absorbers Checked materials in subcomponents using geantino scans. Spikes at Ecal absorber. Is this a bug?.

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Delving Deeper into Geant4

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  1. Delving Deeper into Geant4 Guilherme Lima DHCal Meeting October 22, 2003

  2. Updates since last report • Studied the spikes on the distributions of energy depositions in ECal and HCal absorbers • Checked materials in subcomponents using geantino scans

  3. Spikes at Ecal absorber Is this a bug?

  4. Low energy EM Physics at play 70 + 441 = 511!! 511 keV 69.5 keV Eγ = 511 keV in e+e- annihilation 441 keV ΦW = 69.5 keV ? (photoelectric effect in tungsten)

  5. Why is the Eγ splitted sometimes? Cell boundary γ e- PE energy deposition is assigned here in LCDG4 PE happens here

  6. Spikes at Hcal absorber MIP peak 511 keV zoom in green 7.11 keV 504 keV

  7. Geantino scanning • Purpose: compare radiation lengths (X0) and interaction lengths (λI) to make sure that materials are the same in Mokka and LCDG4 • No φ-dependence (cylindrical symmetry) • θ- and track-length dependences are shown

  8. X0 dependence on θ (SDJan03) Big discrepancies in the forward regions? Comparisons so far

  9. λI dependence on θ (SDJan03) Big discrepancies in the forward regions? Comparisons so far

  10. X0, λI along track length at θ= 90°, φ= 90° Muon Tracker Coil VXD HCal ECal

  11. X0, λI along track length at θ=5°, φ=90° Last detector component

  12. X0 differences at θ = 5°, φ = 90° Differences are quite small

  13. Comparing apples to apples… • Geant version 4.5.2 (new server) • Geometry (SDJan03, projective) • Physics list: identical data files • Range cuts (0.1mm) • Same events are processed in both detector simulators (single particles: 50 GeV e, μ, π) input from binary stdhep file: θ = 90°, flat in φ • Geant4 external data files not used • Materials (some minor differences, should never give significant differences in results)

  14. Conclusions • Peaks at Ecal and HCal absorbers are due to e+e- annihilation in association and photoelectric effect • Materials in LCDG4 and Mokka are in very good agreement • Some low-level discrepancies remaining in both ECal and Hcal need to be understood Should we go for Geant3 cross checks?

  15. Next steps • Fix to energy contributions per cell (lcdg4) • Further investigation on the origin of discrepancies • Look at some complex physics processes • Think about digitization (energies into ADC counts)

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