GlueX Start Counter Meeting, May 31, 2012

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GlueX Start Counter Meeting
Thursday, May 31, 2012
10 am EDT
JLab: CEBAF Center F326/327


  1. Announcements
  2. Review minutes from previous meeting
  3. Mechanical Design
  4. Read-out design
  5. Simulation
  6. Contract

Communication Information

Video Conferencing


Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2012-2Q on the JLab CUE. This directory is accessible from the web at .



  • FIU: Werner Boeglin
  • JLab: Chuck Hutton, Mark Ito (chair), Tim Whitlatch, Beni Zihlmann


Puneet Khetarpal has started work on rate studies with the new start counter geometry.

Prototype Tests

Werner reported test results on the new counter from McNeal. They are getting about 200 ps resolution from the upstream end and 400 ps from the downstream. The average is about 350 ps. This is very near the design goal. SiPM's were used for the read-out with no wrapping on the scintillator. It seems that McNeal did a good job polishing the edges of the scintillator. There were some scratches on the flat sections but they appear not to effect performance.

Puneet would like to confirm in simulation that good edge quality results in good resolution but it is not obvious how to make a volume in Geant4 that has different surface quality on one face versus another.

Werner is looking forward to trying out the new SiPM read-out system when it becomes available.

Mechanical Design

Chuck showed about a dozen pictures of the latest mechanical design. A compromise was reached with the target design guys that resolved the space problem with the cable connector. The design has progressed a lot; we now have a model that will work in principle.

Werner pointed out that the first step is to machine the inner foam support mandrill and glue it to the metal support tube upstream of the counters. Then the scintillators can be placed on the mandrill, with reflective material between the counters, and the whole thing secured on the outside with some sort of banding or wrapping.

For now we are assuming that we do not need any foam on the outside of the counters, even though that foam was present in the CLAS design. This will reduce the amount of material seen by particles. Chuck and Mark will check with Youri Sharabian to see if there was a compelling reason to have the foam on the outside. In the nose section, we will see how much of the inner foam can be removed at the far downstream end, again to reduce the amount of material, while maintaining mechanical stability.

We discussed the division of labor for manufacturing, assembly, and test. Although FIU does have a machine shop, we formed a consensus around having the foam mandrill and support tube machined and glued at JLab, shipping the assembly to Florida, and having FIU assemble the scintillators, plug in the electronics, and test the system. FIU would also be responsible for designing and building any jigs or tooling necessary to perform the assembly and test.

Werner would perhaps like to build a three-counter prototype to practice assembly and gain experience with a fully-loaded SiPM read-out board (three channels per board). He will be in contact with McNeal to give them feedback on the counters delivered and to order more for the prototype. This order will also allow us to see if McNeal can reproduce the good quality of the one non-crazed counter they delivered.


No action yet. Things are getting late. Werner will be at JLab next week and he and Mark will get the ball rolling.