Page History

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• 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 can 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

We see discrepencies in the existing Merit ntuple from several sources.   In order of importance:

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

 Here is a page that describes so efforts to use the new variables to do background rejection.

Improvements to event display

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

Testing and Comparison

  Merit Variables that stayed exactly the same

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