1. MuonGeoModel – recent developments
Most of the clashes observed are due to “artificial” overlaps of station envelops with inert materials
station envelops of a standard shape (trapezoid) are suitable for a hierarchical description of the geometry:
Muon Envelop stations components (MDT, RPC, TGC, CSC, and also CRO, CHV, DED, ect.) with transforms defined w.r.t. a station frame
sometimes small components (cro, chv) at the “border” of a station require a large envelop of the station (almost empty) which, then, conflicts (at the center) with other structures
Geo2G4 transforms any volume in GeoModel (also station envelops made of air) in Logical G4 volumes (overlaps generate unpredictable result of the tracking process)
G4AssemblyVolume is a helper class which allows several logical volumes to be combined together without common mother envelope
Recently, functionality has been added to Geo2G4 in order to allow GeoModel volumes made of “Ether” to be transformed into G4Assembly volumes (i.e. in G4 the station envelop disappear if the station material is declared “Ether”)

2. MuonGeoModel – recent developments
Minimal changes are required in MuonGeoModel to describe stations as assemblies in G4 BUT there’s one important drawback: copy numbers of assembly components are lost
a different identification scheme has to be setup
the Muon Sensitive Detectors have to be modified to conform to the new scheme
MuonGeoModel allows to describe stations as assemblies if a switch is activated
Station copy numbers (embedding StationPhi and StationEta) are modified – used as base for assembly components copy numbers, must be positive and large
in G4 assembly components are given names like
“av_WWW_impr_XXX_YYY_ZZZ_ID” where
WWW – assembly volume instance number
XXX – assembly volume imprint number
YYY – name of the placed logical volume (will keep track of station Type, subType and Techn.y)
ZZZ – logical volume index inside the assembly volume
ID – GeoNameTag: will keep track of info like doubletR, doubletPhi, Swap flag (for Rpc), multilayer (for MDT and CSC), stationEta and Phi (for Tgc)
_ID is new; introduced for our needs in a
ATLAS version of the relevant G4 class

3. MuonGeoModel – recent developments
a modified version of the Muon Sensitive Detectors has been setup to test the simulation
successful exercise but the memory allocation for a simulation with MuonSpectrometer only is ~550MB, compared to previous ~350MB unaffordable at the moment
Many thanks to A. Dell’Acqua and V. Tsulaia for the cooperation and the necessary developments in Geo2G4 and Atlas G4
MuonGeoModel contains a few other changes:
fix of BOG tubes numbering (hopefully solving the hits out of position observed at reconstruction level)
special shape for MDT multilayer (with half tubes removed or added at the extremity of tube-layers) in order to remove clashes between stations in contact (when assemblies will be viable)
Needs testing and fixes for 2 more known and trivial clashes
ready to start testing R’ and R’’ light - no obvious outcome with the database tag available ~15 days (including Easter) before release