GlueX Start Counter Meeting, January 29, 2015

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GlueX Start Counter Meeting
Thursday, January 29, 2015
10:00 am EST
CEBAF Center F326/327


  1. Announcements
  2. Review minutes from the January 22 meeting
  3. Calibration
  4. Plans for Spring run
  5. 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: Eugene Chudakov, Mark Ito (chair), Eric Pooser, Simon Taylor


  • Mahmoud continues to work on the timing calibration.
  • Eric is writing a plugin that selects two paddles with exactly one hit each to measure time resolution.
  • Eric is also starting to look at measuring efficiency.
  • Werner remarked that we need to associate a start counter hit with a track for many of these studies. Eugene noted that we could survey the start counter using tracks to check the position of the counters. We could also start using the tagger to nail down timing.
  • The anomaly at 180 degrees in phi remains.
  • Simon found the cause of the vertical bands (lines of constant z) in the distribution of intersection points between tracks and the start counter when projected in the r-z plane. They are coming from particles at forward angles that miss the start counter. The algorithm often breaks down in these cases.
  • Simon also understands the "fuzz" in the distribution on the downstream side of the nose section. This comes from an overly generous cut in phi to associate tracks with a counter. Matches with a counter far from the track in phi put the intersection point outside the counters.

Mounting ST to Hydrogen Target

Eric showed some slides illustrating a mechanical problem discovered when an attempt was made to mount the start counter to the hydrogen target cart. Bolt heads on the target cart interfere with the start counter mounting flange. The flange on the target cart is glued to the scattering chamber[?] and is not easily replaced. The solution is not clear at this point. We agreed that we should resist and drilling or grinding on the start counter assembly.

We will talk to Tim to make sure he is in the loop in coming up with a solution and express our opinion that the start counter should be left alone.