Page History

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• Use pattern recognition in addition to GEANT model to determine which tiles and ribbons to associate with tracks
  • This allows us to handle near misses, which is needed to do efficiency studies.   An start on one such study is here.
  • More detailed description of pattern recognition technique is here
• Have information be associated with tracks, instead of having a single big set for the whole event
  • This makes using the event display much easier
  • This makes getting access to information in Recon root files easier
  • More information about new ACD recon data structures is here
• Handle track errors correctly
  • This wasn't being done before
  • This looks nice in the event display
  • More information about error propagation is here
• Sort ACD - track associations by a combined signal size/ distance quality measure instead of using only distance
  • This gets rid of problems with shadowing, where one association with a small signal masked another nearby one with a larger signal
  • More information about quality measures is here
• Always calculate gaps to tiles
  • Before this was a hodge podge, we had to handle cases where the track hit ribbons, tiles and missed everything differently.
  • More information about how we treat gaps is here
• Sort gaps by the probability that the track went into the gap, including the size of the gap and the error projection
  • Before gaps were sorted only by the distance to the gap

  Minor Changes

In the process of  doing all this work a couple of smaller improvements presented themselves:

• Change the way the distance of closest approach is calculated when the POCA occurs exactly at the head of the track
  • This effects some events track which graze side tiles (and a very few which graze to tiles), but only when the distances of closest approach is quite large
• Use the hardware veto information instead of the energy information in counting number of tiles hit in the Merit Variables
  • This handles issues with the slower timing of the PHA electronics

  New information in Merit ntuple

  We wish to add some new information to the Merit Ntuple.  Mainly this is information about the combined signal size and track projection estimator of how likely a given tile is to veto a track.   

  Noticable changes in existing Merit quantities

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1. We changed the way the "best" track-tile, track-ribbon and track-gap associations are selected.   This causes some small fraction of the events to have changes in a couple of merit variables.   The effects are different various cases.  Here is a page that summarized the effects.
2. We change the way we report the point of closest approach when it occurs at the head of the track.  This affects tracks near the sides an top of the LAT with high incident angles w.r.t. the tiles or ribbons.  Here is a page that describes this in more detail.
3. We use the hardware veto bit directly to count hits in the various parts of the ACD.  Before we were using the signal size that was equivalent to the intended veto threshold.  This causes a few events to move around in the various counting variables.
4. We set an upper limit of 10000 sigma for all associations.   This causes a few events with large negative active distances to return to the default values of -2000.

  Effects on background rejection

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Here is a page that describes how this information is visualized in the event display.

 Path Path towards deployment

Here is a page that describes the issues with and suggests a path towards deploying this stuff 

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