GlueX Start Counter Meeting, June 30, 2016

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GlueX Start Counter Meeting
Thursday, June 30, 2016
10:00 am EDT
CEBAF Center, Room F326/327


  1. Announcements
  2. Review minutes from the last meeting
  3. Calibration Update
  4. NIM/TDR
  5. 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: Mahmoud Kamel
  • JLab: Mark Ito (chair), Simon Taylor, Beni Zihlmann
  • NU: Sean Dobbs

Update on Efficiencies

Mahmoud presented slides on the latest results from his efficiency studies. He used a ROOT tree produced from the start counter efficiency plugin run as part of the production reconstruction pass on the Spring 2016 data. A single file was analyzed. See his slides for the plots. His slides covered:

  • criteria for selection of charged tracks in the study
  • histograms of some global properties of the tracks and start counter hits
  • start counter efficiencies for all tracks: 98%
  • histograms of the same global properties when a phi cut is applied to tracks to keep them away from the edges of the counters (delta phi cut)
  • efficiencies with the delta phi cut: 99%
  • same efficiencies for the straight section: 99%
  • for the bend section: 99%
  • and for the nose section: 99%
  • the studies were repeated for protons, pi+, pi-, and K+
  • for K+ no start counter misses were found when the delta phi cut was applied; the study was repeated without the cut

Efficiencies are everywhere (almost incredibly) high.


We asked Mahmoud to think about documenting the calibration procedure in a cookbook-like fashion so that future students will be able to reproduce it.

Dark Rate Monitoring

Beni brought us the issue of monitoring dark rate of the SiPMs. We don't have a regular procedure for doing so. This is important given the start counter's proximity to the beamline and Yi Qiang's study that degradation can occur with exposure to the beam. We will have to develop a way to keep track of this.

Mcsmear Parameters

Sean reminded Mark and Simon that they promised to come up with a sensible parametrization for the smearing function.

He also mentioned that there is no run-dependent time resolution currently in the CCDB. Mahmoud has seen evidence for small shifts, but has not done a detailed time-dependence study. He will have a look, hopefully before the end of July.