GlueX Start Counter Meeting, August 13, 2015

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GlueX Start Counter Meeting
Thursday, August 13, 2015
10:00 am EDT
CEBAF Center F326/327


  1. Announcements
  2. Review minutes from the August 3 meeting
  3. Start counter efficiency calculations
  4. Calibration
    1. Attenuation Calibration
  5. DAQ Tasks for Spring 2015 Commissioning Run
  6. Action Item Review




Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2015 on the JLab CUE. This directory is accessible from the web at .



  • FIU: Werner Boeglin, Mahmoud Kamel
  • JLab: Mark Ito (chair), Eric Pooser, Simon Taylor

Review of minutes from the August 3 meeting

We went over the minutes.

  • Eric has started on the GlueX Note describing the calibration procedure.
  • For the time propagation correction he has decided to use the measured delays[?] rather than a set velocities with a different velocity for each region.
  • Eric updated the PID library to use the final versions of the calibrations. The CCDB has been updated as well.
  • The resulting time resolution is 60 ps below design for all 30 paddles.
  • Eric pointed out that a years has gone by since construction and there is no visible deterioration of counter performance. Recall that in the past degradation was apparent after a few months.

Start counter efficiency calculations

Mahmoud presented slides describing how he determines efficiencies and how the method has improved from previous attempts. See his slides for details.

Simon pointed out that, unless explicitly turned off, there are a lot of tracks that get their t0 from the start counter. For these tracks, the existence of start counter hit is therefore a given and the efficiency might be artificially high. Mahmoud will check whether this association between tracking and the start counter was on or off (off: USE_SC_TIME=0).


Eric gave us an update on the calibration effort, in particular the attenuation correction. For details see his slides.

For work with the data he incorporated the path length correction and is now calculating dE/dx (literally). The distributions tighten up considerably. He has success fitting the distributions to Vavilov distributions. The problem with a lack of statistics at the upstream end remains however. He settled on using the attenuation values measured on the bench at FIU for the corrections.

With the updates to the PID library to apply all of the calibrations, Sean Dobbs asked about the plan for installing calibration constants in the MC variation. Eric has started looking at how the hits are created in HDGeant. The idea is to apply constants that reverse the process applied in event generation.