Based on a presentation of M.Verderi Cuts per region John Apostolakis, 15 Nov 2002 Layout Introduction Generalities Analysis Design (skipped) Plans Based on a presentation of M.Verderi

I. Introduction Cut in all G4 & here = «production threshold», Not tracking cut; GEANT4 originally designed to allow a unique cut in range; Unique cut in range per particle; Default being a same cut for all particles; Promotes consistency of physics simulated A volume with high cuts (ie poor physics quality) will not «pollute» a neighbouring volume with low cuts; But requests from ATLAS, BABAR, CMS, LHCb, …, to allow several cuts; Globally or per particle;

II. General considerations

Cuts for what ? Some physics processes involve infra-red divergences; Bremsstrahlung; Infinity of lower and lower energy photons; Ionisation; Huge number of low energy electrons; Limited by the (low) ionisation potential; Goal of cuts is to limit the discrete production of secondaries; Corresponding energy is transfered to the continuous component;

Today’s picture On the user side: On the G4 kernel side: User constructs a detector: Volumes Materials (S)he defines the physics processes to be used; And then sets the cut; Cut in range for the all simulation; Eventually the cut may depend on the particle type; On the G4 kernel side: For each particle, G4 triggers the conversion of the cut in range into the equivalent energy threshold; For each material; Processes can then use these thresholds to compute their cross-section tables; One table per material;

Analysis

Motivation for several cuts Having a unique cut can be the source of performance penalties; Part of the detector with lower cut needs fixes the cut for the all simulation; Can be far too low than necessary in other parts; Silicon vertex detector: a few 10 mm; Hadronic calorimeter: 1 cm; Other parts being geometrically far, to.

Relaxing the unity of range cuts Request to allow several cuts has been analysed as follows: A cut value is typically required at the level of a detector sub-system: Silicon vertex detector: a few 10 mm; Hadronic calorimeter: 1 cm; Introduce the concept of « region »: Large geometrical area,typically the root logical volume of a sub-system; Or an group of root logical volumes; Eg: barrel + end-caps of the calorimeter; A cut in range is associated to a region; Eventually a range cut per particle is allowed;

Snapshot of detailed design (Skipping in the interest of time)

IV. Status

Anticipated limitations Partition of logical volumes; The same logical volume can not belong to two different regions G4ProductionCut defines a set of cuts for all particles; Some potential duplication exists The same cut value can appears for, say electrons, in two different production-cut objects; And some materials appear in the related regions; In this case cross-section table will be calculated twice; This is a considerable complication The current design does not take it into account; Consideration is left to a future design iteration.

Status Detailed design for cut per region has been made; It does not imply severe design revision of the existing GEANT4; About the plans: Development release(s): 1Q 2003 Target scheduled release: June 2003.