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Enhanced Parameterisation of EM Showers in ATLAS LAr Calorimeter

Fast simulation of ATLAS LAr calorimeter using LArFastShower derived from G4 class FastSimModel. Testing with ATHENA 10.3.0 and G4AtlasApps. Comparison of timing results between original and new simulation schemes. Investigating direction changes in electrons. Impacts on physics performance. Optimization of "kill" cuts for performance improvements.

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Enhanced Parameterisation of EM Showers in ATLAS LAr Calorimeter

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  1. Parameterisation of EM showers in the ATLAS LAr Calorimeter Tom Atkinson - The University of Melbourne On behalf of Elisabetta Barberio - The University of Melbourne Anthony Waugh - The University of Sydney

  2. Introduction • Fast Simulation of ATLAS LAr calorimeter implemented in package: • LArCalorimeter/LArG4/LArG4FastSimulation • Class LArFastShower derived from G4 class FastSimModel • Depends on LArCalorimeter/LArG4/LArG4Barrel • EMBParticleBounds • EMBShowerParameters • Simulation testing done with ATHENA 10.3.0 • G4AtlasApps-00-00-31 • New tag LArG4FastSimulation-00-00-05 • Hacked version of LArG4Barrel/src/EMBParticleBounds.cc • NB: New tag produced LArG4Barrel-00-00-56 but not backwards compatible against 10.3.0

  3. Original simulation scheme • Timing performance previously significantly worse in full ATLAS simulation vs stand-alone reconstruction. • Original simulation scheme: This scheme was fine for stand-alone testing of the calorimeter - no showering!

  4. Original simulation scheme - Timing results • But showering occurs in ATLAS when particles generated at nominal interaction point. • Large numbers of low energy shower particles also entering the calorimeter • Result is a large increase in execution time. • ATLAS scan range -0.8 <  < 0.8 (NB: Full simulation in crack) • 100 events per sample Average time / event

  5. Timing vs.  - original scheme

  6. New simulation scheme This scheme is not final. Cuts on “kill” limits will change as we optimise performance vs. timing…

  7. New simulation scheme - Timing results • Electrons generated at nominal vertex • -0.8 <  < 0.8 (NB: Full simulation in crack) • 100 events per sample Average time / event

  8. Number of Parameterisation method calls Original scheme/new scheme

  9. Timing tests in the ATLAS endcap • Electrons generated at nominal vertex • 1.5 <  < 2.5 • New particle simulation scheme used Average time / event Under investigation - more complex geometry!

  10. For discussion… A word on the direction of electrons… • LArFastShower::ModelTrigger() Get Momentum Direction:(0.576413,-0.816949,-0.01849) • LArFastShower::ElectronDoIt() Get Momentum Direction: (0.788559,-0.609188,-0.0840549) • Change of direction between ModelTrigger and DoIt seen for electrons ONLY • (Positrons and photons seem to be ok) • Consistent with effects seen by CMS Does anybody know what causes this?

  11. Conclusion • Significant improvements in timing when low energy electrons and photons from the shower are “killed”. • Impact on physics performance of new scheme is currently beginning. • “Kill” cuts will be set to optimise performance vs. timing TheEnd…

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