1. 0 Status of Shower Parameterisation code in Athena Andrea Dell’Acqua CERN PH-SFT

2. 1 Who  Most of the implementation work (and interfacing to Athena) done by Anthony Waugh (Univ. of Sydney) Still willing to spend a significant fraction of his time on this subject but shifting emphasis  State of the art presented by Anthony at the recent LAr week Available at: http://indico.cern.ch/conferenceDisplay.py?confid=a062981 http://indico.cern.ch/conferenceDisplay.py?confid=a062981  Most of the gibbering here by me Apologies if I misrepresent anything/anybody

3. 2 What  Use G4 parameterisation interface “as is”  Re-implement G4Flash-like shower parameterisation procedure and customize it to the case of ATLAS LAr calorimeters  Concentrate on the LAr calorimeters There is no reason why Tilecal can not be included, it was just a (wo)manpower issue until now  Stick to EM physics yet Is there a need of parameterising hadronic interactions? Is there a safe way of parameterising hadronic interactions in ATLAS?

4. 3 How  Fast simulation scheme Only electrons/positrons are parameterised. Photons are followed by full sim. up to the point they convert (only then parameterisation kicks in) Particles must be within allowable energy range, if not use full simulation Shower must be contained within the calorimeter, in Z(95%) and R(95%). If not return to full simulation. When a fully contained electron is produced, it is parameterised Showers starting before the calorimeter are handled by full simulation. Each particle entering the calorimeter is then handled separately by parameterisation mechanism

5. 4 How (2)  If all boundary conditions are satisfied The track is killed Fake steps (10  m) are simulated along the initial electron trajectory. Energy deposited and nr. of spots per steps are calculated Sampling fluctuations are calculated, according to calo resolution Energy and position of each spot are calculated Fake steps are filled up and given to (standard) sensitive detector classes to generate hits Standard simulation chain utilized to process hits Loop until the total shower energy is deposited

6. 5 Full vs. Fast  Shower profiles for EM barrel (10GeV e-)  BLUE - Full sim. RED - fast sim.

7. 6 Full vs. fast (2)  Shower profiles for EM endcap (10GeV e-)  BLUE - Full sim. RED - fast sim.

8. 7 Full vs. fast (3)  Shower profiles for FCAL (10GeV e-)  BLUE - Full sim. RED - fast sim.

9. 8 Simulation time  Shower simulation time (electrons) for full and fast simulation

10. 9 What is available?  In release 12.0.1 All machinery in place and working Add (to standard job options) SimFlags.CalibrationRun.set_Value('') … AtlasG4Eng.G4Eng.add_FastSimModel("LArG4FastSimulation","LArFastShower","LArMgr::LAr::EMB::STAC") AtlasG4Eng.G4Eng.add_FastSimModel("LArG4FastSimulation","LArFastShower","LArMgr::LAr::EMEC::OuterWheel") AtlasG4Eng.G4Eng.add_FastSimModel("LArG4FastSimulation","LArFastShower","LArMgr::LAr::EMEC::InnerWheel") AtlasG4Eng.G4Eng.add_FastSimModel("LArG4FastSimulation","LArFastShower","LArMgr::LAr::FCAL::Module1::Absorber")  Parameterised models CAN NOT be used together with calibration hits (obvious) but they don’t seem to go together with dead material hits either! To be understood and fixed…  Currently limited to LAr calorimeters only  Event sample (single particles) to be added to the standard test production exercise

11. 10 What remains to be done?  Extend shower parameterisation to Tile/HEC/HadFCAL  Repackage code (currently in LArCalorimeter/LArG4/LArG4FastSimulation )  Make steering parameters accessible via python/JO  G4 8.x coming along, require interface change (backwards incompatible)  Test, validate, improve Single particles, full events EM component of hadronic showers Different (coarser?) parameterisation models Speed?  Understand physics requirements and figure out physics channel specific parameterisation strategies  Where can we gain? How much? Is it worth the hassle?