SSD and the global reconstruction chain SVM EST EGR SAL

EST Progress and information about the new EST can be accessed here !
In order to overcome the difficulties encountered with the SVT tracking method when the SSD is taken into account, a TPC to SVT Tracking (EST) module has been developed. Unlike the current strategy (based on separate trackings in the TPC and the SVT followed by a track matching), the main idea is to start with the TPC tracks and to try to extrapolate them with hits in the silicon vertex detector. More specifically, the main structure is the following :

- 5 passes looking for various hit segment sizes :
  • at least one hit in each layer
  • at least one hit in each layer with extended searching areas
  • at least one hit in 3 different layers
  • at least one hit in 2 different layers
  • at least one hit in the SSD
- In each passe, 7 iterations over different transverse momentum threshold
starting from the highest momentum tracks.
- During each iteration, several steps are performed :
  • Projection of the TPC tracks on the SSD
  • SSD hit - TPC tracks association (geometrical criteria)
  • Tracks refitting with the new hit included
  • 3 first steps for the SVT layers

The module is currently written in Fortran and can be found here (in the directory pams/global/est). This module can be used to replace in the chain SGR/STK and SVM. Besides its own output table, EST fills the STK and SVM output table and can followed by the global refitter (EGR). Fairly good performances have been obtained with EST which are commented in the "SSD and Tracking" section. However the current version has several drawbacks which summarized below :

  • Working and satisfactory performances but...
  • Primary tracks : OK but not better than the old SVT code
  • Secondary tracks : large increase of reconstructed tracks but too many ghosts
  • Slow and (static) memory consuming
  • Barely changeable. Any change leads to inconsistent results

All these disadvantages have lead us to start a major revision of the module. The specifications of this new version are the following :
  • Working and performing well (speed and efficiency)
  • Integrate and complete tracks coming from other tracker (sgr, stk)
  • The basic principle is the creation/deletion of branches
  • Integrate and can use the dE/dx info of the SVT and SSD hits
  • Allow hit sharing between tracks
  • Complete the SSD hit reconstruction (p-side and n-side cluster association may be incomplete after the hit reconstruction module)
  • Identify working intervals. Its performances must be known in function of the particle multiplicity, the particle species, the mean momentum, the position resolution in the wafers, the TPC tracking efficiency,...
  • The code should be documented and easy to use (the main options should be easy turn on/off)
  • Working and debugged as soon as possible

This page will be updated once a working version of EST is available.



A study on the internal alignement of the SSD combined with the SVT has been initiated using the SAL package. The status of this study is reported in these pages

Last modified: Fri Dec 8 17:39:02 CET 2000