Tracker hits reconstruction

Normally a particle fires several strips as it passes through the detector so that the hits are formed by clusters of fired strips. This involves a cluster finding algorithm and conversion from strip number system to detector local system.

Reconstructed hits are stored in RHIT structure which is a CMSIM home made structure imitating the standard GEANT structures HITS and DIGI. The RHIT format is explained in section 5.3.3. Routines GSRHIT, GPRHIT and GFRHIT are used for storing, printing and retrieving the entities from the RHIT structure. These routines are found in //util/uthits.

There are two different options available for hit reconstruction:

1. Hits reconstruction from HITS by Gaussian smearing
2. Hits reconstruction from DIGI structure by strip clustering

The option 1 is used when one wants to bypass the more time consuming detailed digitization simulation HITS DIGI. The smearing method is also useful for checking the event reconstruction codes, because in smearing method one knows exactly the point error matrix: it is the one used in smearing.

The program flow is as follows:

              GTRIG
                 CMRHIT        (Steering)
                    CMD2R      (option DIGI -> RHIT)
                       TPD2R   (Pixel)
                       TSD2R   (Si)
                       TMD2R   (MSGC)
                       MUD2R   (Muon)
                    CMH2R      (option HITS -> RHIT)
                       CMH2R1

 
• Pixel hits reconstruction