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Online Pattern Recognition

 

Online pattern recognition in the CTD is performed in two dimensional projections. Hits in the transverse r- tex2html_wrap_inline810 projection are obtained by knowing which axial sense wires were hit and using a planar drift approximation. Although the stereo layers will give precise measurements of track polar angles ( tex2html_wrap_inline812 ) and beam-line vertices (z) this information cannot be decoded until the track finding in the r- tex2html_wrap_inline810 projection is completed. This is too time consuming for the trigger so some axial layers have been instrumented with z-by-timing electronics enabling r-z information to be available to the trigger.

The CTD SLT works in the r- tex2html_wrap_inline810 plane to determine the number of tracks in the event, their tex2html_wrap_inline798 , origin, and the event vertex, while the FLT supplies rudimentary r-z hit patterns. The SLT two dimensional r- tex2html_wrap_inline810 information will be correlated with the FLT z-information for full three dimensional pattern recognition or consistency checks between the two trigger levels. At present the CTD-SLT pattern recognition works exclusively with the axial r- tex2html_wrap_inline810 projection but will eventually include z-information.

Parallel processing is exploited in the r- tex2html_wrap_inline810 track finding. The layered structure of the wires in the CTD allows the eight sense wires in an axial superlayer to be used to form track segments which are labeled by their position and direction, these are called vector hitsgif. Segment finding is a local operation and can be performed in each cell independently. By exploiting parallelism the method has the advantage of reducing the amount of data that must be handled in each pattern recognition step.

The CTD-SLT track finding algorithm is thus split into two stages.

  1. Search for track segments locally in cell masks.
  2. Match the local segments to form global tracks.

In this note we will discuss in detail the segment finding algorithm, while the segment matching is only briefly mention and will be described in a future note. Figure 2 show the Entity Relationship Model diagram of the CTD-SLT system. The actual online data formats proposed for the system are described in reference [3].

  figure31
Figure 2:   Entity Relationship Model for CTD-SLT system.




next up previous
Next: Segment Finding Algorithm Up: Segment Finding Previous: CTD Second Level

Douglas M. Gingrich
Thu Mar 28 18:08:05 MST 1996