CDC Future MC Studies Discussion, October 1, 2008

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Participants

  • Carnegie Mellon: Curtis M.
  • Jefferson Lab: Elke A., Mark I, David L., Elton S. and Beni Z.

Presentations

Elton presented the results of his studies of straight tracks going through the various geometries for the CDC. In doing this, he looked at all possible "local" left-right combinations and computed the chi-square from the hit residuals from these, and from the resulting fit track parameters. His figure-of-merit had to do with how often more than one left-right combination gave a good track fit. The conclusions were that the base-line design was not particularly good in terms of having a good geometry, and that either close-packing, or shifting the layers could substantially improve this. It also appears that having sufficient local information helps in this as well. For all the changed geometries, four layers of the same type appeared to be sufficient. In the close pack, it looked like 3 was still OK. This would lead one to conclude that choosing four with the close-pack would allow for a hit inefficiency without a substantial loss in efficiency.

Mark presented the results of his fitting algorithm. The basic idea is a two-pass method that allowed the fitter to decide what the correct left-right choice was. This was accomplished by designing a penalty function for the first pass that only penalized moving away from the wire, moving towards the wire, to the same place on the other side introduced no penalty. This function is used in the first pass. The second pass then implements a more normal penalty function. The examples that mark showed were based on the reference CDC geometry and showed that the two pass method made a substantial improvement. Mark feels that some of the remaining problems are due to poor starting values for the track parameters---the ones that are taken now are rather course. Mark planned to try to improve these choices. Other suggested things to try are to use some of the modified CDC layouts and to see what charge division of the order of +-6-7cm would do.