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