General

The organisation of work with the geometry, material and tracking media constants in CMSIM are based on the following principles:

1. All detector geometry related constants are defined in external files. TZ (ZEBRA Title package format) titles are used as initial storage for these constants. The detailed format of the title banks may be detector dependent.
2. The constants are considered first of all as instructions for direct filling of the corresponding GEANT structures - volumes, materials and tracking medias, rotation matrices, detector elements definition and detector dependent information for description of the corresponding detector element response. At this stage title constants define objects corresponding GEANT entities with parameters as attributes of these objects.
3. The geometry defined by these titles (GEOM/GEAN banks) is built with the TZ utility routines in source module. Experimental hall, master-volume for all subsystems, as well as volumes not belonging to a specific subsystem (e.g., quadrapole, shielding, etc) are defined in the same way.
4. The geometry definitions include information to allow for version selection.
5. There is a set of standard rotation matrices defined by ROTM title bank with a 4-character keyword for each matrix. A standard rotation matrix is accessed by using this keyword in a call to a utility routine. This set includes as ``NEXT'' or ``xNXT'' for any additional rotation matrix. For the additional rotation matrices an identifier number is given incremented by one from the largest number so far.
6. Material and tracking media are always referred by there name

The approach has been introduced and discussed in detail in a previous technical note[14]. As has been pointed out above, in CMSIM all experimental setup related code and constants (geometry, material, rotations, hits - formats, magnetic field map, user-defined detector parameters, ) are centralised into the three following sources (see flow diagram in section 2.3):

• The source module (DETector Constant) with FORTRAN routines which contain all non-trivial parametrical models for all subsystem (detector) descriptions.
• The module (TITLe information for the detector) which contains in the ZEBRA Title Package format (TZ-format) all constants and user parameters for the above models. The magnetic field maps are also in module. A short description is given in the next section.

The title banks with information on geometrical parameters carry the global version number to which they correspond (through the user selection flag). The non-trivial part is an interface between the TITLes data banks and the FORTRAN codes (from DETetector Constant module) describing the model for a specific sub-detector. To establish that we define title banks of two types:

• Title banks which contain parameters
• Title banks of specific formats for volume definitions which are interpreted by specific utility routines of the package. In fact there are two styles of format definitions which are used:
  • ``GEOM'' style in which we define the main detector volumes as polycones or polygons and if there exist a parameter title bank with the same name and the same version then it is required an action from the FORTRAN codes.
  • ``GEAN'' style contains a bunch of trivial GEANT instructions like creation of volume, its positioning, hit definition, detector set definition, setting an attribute to the volume, and so on.
  Only the above two types of title banks have assignment to keywords and version numbers which have been discussed in the version selection mechanism (see section 1.5).

As an example, shown in Fig.3.1 is a drawing of the CMS detector obtained in GEANT using the above title banks.

  
Figure 3.1: The CMS detector GEANT description.

The formats of the title banks will be described in detail below.