Basic framework

The software is organized firstly in terms of functions and secondly in terms of subdetectors. Here are some of the basic features listed:

• the high level steering routines are in the module
• the constants for detector description are in module
• the routines dealing with the 'title' constants to build the detector are in
• hit definitions for all tracking detectors - the Central (Inner) tracker and the Muon system (which is considered to be the Outer tracker) - are unified and the differences among the specific detectors appear only in the digitization and cluster reconstruction stages. The format of reconstructed hits is the same for the all tracking detectors in CMS.
• simulated hits are stored in HITS structure
• detector responses are simulated and stored in DIGI structure
• reconstructed hits are computed from DIGI and stored in CMSIM customized structure called RHIT which is similar to HITS and DIGI
• all structures HITS, DIGI and RHIT are customized from standard to have separate sections according to LHC bunches where the hits originate from

The basic goals for full CMS simulation are the following:

• to create an adequate computer model of the detector
• to simulate the detector response up to the level of the data that will be obtained from the CMS DAQ system
• to reconstruct events in order to provide the reliable estimation of detection efficiencies of e 's, 's, 's and jets.

At least three levels of detail must be provided for different subdetector simulation models:
fast simulation - geometrical acceptance + parametrical model for detector responses
so called ``mixture'' level simulation - dead materials, background estimation and
reconstruction
full simulation - detailed event simulation up to the DAQ level accounting for event
pile-up effects.
It is important to note that a consistent simulation must be provided at each of these different levels. An essential component of the computer model of the detector is the ``data base'' consisting of the following elements:
a description of the detector geometry
the magnetic field map
all material and tracking media definitions
sensitive element definitions
definitions of ``hits'' providing the information required
for the digitization stage and event reconstruction
the tools necessary to work with this data base Details are described in the following sections and in the Reference Manual which follows. Information on administration and maintenance of the CMSIM system is given in Appendix A.1.