GlueX Start Counter Meeting, April 21, 2016

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GlueX Start Counter Meeting
Thursday, April 21, 2016
10:00 am EDT
CEBAF Center, Room F326/327


  1. Announcements
  2. Review minutes from the last meeting
  3. Calibration Update
  4. Run Issues
  5. NIM/TDR
  6. Action Item Review




Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2016 on the JLab CUE. This directory is accessible from the web at .



  • FIU: Werner Boeglin
  • JLab: Mark Ito (chair), Simon Taylor
  • NU: Sean Dobbs

Calibration Update

Propagation Delay Parametrization

Sean Propagation Time Corrections identified an inconsistency in how the propagation time delay was parametrized between data and Monte Carlo. The issue was fixed in Pull Request #338. From the pull request:

  • Make propagation time corrections be consistently defined in terms of path length through scintillator
  • Rewrite plugins to pull expensive calculations outside of locks
  • Other minor changes

Charged-Track/Start-Counter Matching

Sean did a study showing the distribution of azimuthal angle within a single start counter sector versus z where the azimuthal angle is determined by the intersection of the track with the start counter and only track/start-counter matches are considered. Plots were made for each of the 30 sectors.

There is feature in the nose sections where a bias is seen in some counters toward higher or lower azimuth, depending on the counter. The bias direction and amplitude seems to be a smooth function of sector number making geometry a likely candidate for the source of the effect. Without correction we may have to increase the tolerance for a match in the nose region.

Pre-Amp Strain Relief

Although this work was done at the beginning of the run, the photos showing the strain relief system were never shown at this meeting. See the photos and accompanying email from the designer for details.

mcsmear Parameters

We reviewed the parameters again. See the discussion from last time.

In discussing the energy resolution, we noted that we not have a good measurement of the number of photons per MeV and the measured resolution in real data contains both the intrinsic energy loss fluctuations as well as the effect of photon statistics. In Monte Carlo, these effects are put in separately, and so must be disentangled in the data if data is to be a guide.


Werner reported that Eric Pooser has started a TDR contribution for the start counter.