GlueX Start Counter Meeting, August 24, 2017

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GlueX Start Counter Meeting
Thursday, August 24, 2017
11:30 am EDT
CEBAF Center, Room F326/327


  1. Announcements
  2. Review minutes from the last meeting
  3. Calibration and Efficiency
  4. Time-dependent geometry adjustments
  5. Mcsmear procedure and parameters for the start counter
  6. NIM/TDR
  7. Action Item Review




Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2017 on the JLab CUE. This directory is accessible from the web at .



  • FIU: Werner Boeglin, Mahmoud Kamel
  • JLab: Mark Ito (chair), Thomas Britton

There is a recording of this meeting on the BlueJeans site. Use your JLab credentials to authenticate.


Thomas reported that the start counter hits are in HDvis. Hit counters are shown in orange; un-hit counters in faint white. The target has not been added yet. To see the current version, click here.

Review of minutes from the last meeting

We went over the minutes from July 27.

  • Mahmoud overcame the problem he reported last time with modifying the PID library.
  • After putting the new attenuation constants into the CCDB, Mahmoud did not see a significant improvement in the dE/dx measurement. He is repeating the calibration with the new, self-consistent version of the software to see if that makes any difference.

Start Counter Performance Studies

Mahmoud presented his latest results. For all of the details and his plots, see his slides

  • Propagation Time Corrections. Using charged tracks he measures the light propagation time in the counters and fits that time vs. light propagation path length in the counters to a straight line, separately for each counter and separately for the three regions of the counters, straight, bend, and nose.
  • Time Resolution. In a similar procedure he measures the time difference between the start counter hit and the prediction from the charged track taking account of the propagation time as determined in the previous study. If he restricts the fit to a single Gaussian to a region of &plusm; one sigma, he gets an average time resolution of 214 ps. This tight restriction may give a slightly optimistic results. We discussed various ways of getting a more fair characteristic resolution number. We also noted that there is a contribution to the resolution from the charged track timing.

NIM Paper

Mark reported status as told to him by Eric Pooser prior to the meeting.

  • Many plots had to be redone to get publication quality versions. There was some significant computer file archaeology involved, but this work is done. Eric should be done with his parts of the paper by this week.
  • Mahmoud is working on the plots on the attenuation measurements with real data and the attendant text. Those should be ready by the end of next week.
  • All members of the start counter working group should have a look at the paper. It is in Eric's Github repo at
    • At some point we should move it to the gluex-documents repository.
  • We agreed to circulate a draft among collaborations members for comments and author list corrections.