SCF

The first module SSD Cluster Finder (SCF) scans the strip signals on both sides of each SSD wafer in order to build clusters. This module :

• reads and sort the strip signals from the spa_strip table
• searchs clusters by :
  • scanning the strips and looking for a central strip with an amplitude above a given threshold
  • scanning the neighboring strips in the list looking for consecutive strips with respect to the central strip.
• creates a cluster list and add any new cluster
• scans all the clusters and tries to split the cluster by looking for a local minimum in the cluster profile.
• updates and sorts the cluster list and finally stores the cluster in the scf_cluster table.

SCM

The second step is performed by the SSD Cluster Matcher (SCM) module with two main goals : to associate the clusters found on the sides of each wafer and to determine the main parameters (position,energy loss) of the resulting space point.

Silicon microstrip wafers are not real bidimentional detectors and consequently clusters found on the n-side and the p-side of the detector need to be correlated based on some criteria. Depending on the particle multiplicity and their positions in the wafer, such correlation can be non trivial and can lead to ambiguous associations. Hopefully, for a given particle, the charges collected on both sides of the wafer are produced by the same energy deposite and a strategy based on a charge matching can be applied to help to correctly select the true associations.

Depending on the number of clusters on each side (latter on referenced as "packages") involved in this association problem, several configurations can be encountered. They are listed here and the cases 1, 1-2, 2-2, 2-3 and 3-3 are illustrated.

The following steps are performed in the module :

• reading of the clusters from the scf_cluster table
• in each wafer, the cluster matching is started by looking for and creating new packages by mean of geometrical correspondances
• an attempt to solve each package is then made by determining which configurations are possible. The charge matching is then used to assign relative probabilities to each configuration and a given weight to the resulting space points.
• Each space point is then caracterized (x-y-z position,u-v position, energy loss and quality factor) and add to a list
• The space points are stored in the scm_cluster and scs_spt tables.

The list of tables used and methods defined in SCM to perform these steps can be found here. An example of how the geometrical correspondance is applied and how the packages are found is illustrated here. Solutions to apply the charge matching and to assign relative probabilities are shown for the cases 2-2 and 2-3.

SCE

The performances of the hit reconstruction modules will be evaluated with the help of the SSD Cluster Evaluator (SCE) module. The impact of their efficiencies on the tracking performance will be also studied. This module still needs to be written.