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Status of shower parameterisation

Recent updates and developments in shower parameterisation, including fixes, migration to regions, and future developments. Includes information on fast simulation code and the use of ghost volumes.

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Status of shower parameterisation

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  1. Status of shower parameterisation Marc Verderi LLR – Ecole polytechnique Bordeaux, 9th Nov. 2005

  2. Recent past/current news • ATLAS discovered a problem in stepping • Made the “exclusive force” flag not working properly in some situations • Now fixed and released • Migration to region • Fast simulation code migrated to G4Region • Fast simulation models are now attached to the G4Region (through a G4FastSimulationManager), thanks to Makoto. • They used to be attached to an “envelope” (a G4LogicalVolume, root of a volume hierarchy tree) • Envelope and region are close/same concept • Still, example N05 needs to be updated • Must be done quickly • Migration to region implies some changes of the user code: • For what concerns informations related to the “envelope” • Change of G4LogicalVolume → G4Region • GFlash code migrated to G4Region as well, by Joanna

  3. About gflash in G4 • Work undertaken by Joanna Weng • Motivated by CMS needs • Concrete EM shower parameterisation • H1 fortran code, re-engineered to G4 • Up to 2 order of magnitudes speed-up in “block” geometries  • But only factor ~<5 in realistic geometries  • Many parts left to detailed tracking • Many calls to trigger methods of fast simulation • returning “false” : ie no parameterisation • Case of low energy particles in shower • Investigate what optimization could be done on fast simulation code side • Like “forget” a track • Or “forget track and daughters” • Limited gain expected ?

  4. Future developments • The “ghost volumes” capability was part of the requirements for the “parallel geometry” development • “ghost volumes” are used to define regions in which a fast simulation can be triggered, having this ghost volumes independent of the tracking geometry • These geometry are “flavored” : ie defined for given particle types • A parallel navigation is provided currently by the fast simulation process • But complications arise in case of a presence of a magnetic field • The general parallel navigation capability should solve this • Fast simulation will be migrated to this general framework when available • Will/should consist mainly of changes in the fast simulation process. • Informal parallel session on this topic this afternoon 17:00 – 18:15

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