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Parameterisation of EM showers in the ATLAS LAr Calorimeter

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. Introduction.

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Parameterisation of EM showers in the 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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