Time-of-Flight/Start-Counter Meeting, August 7, 2009

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Location, Time

Friday, August 7, 2009
3:00 pm EDT
JLab: CEBAF Center, Room F326/7
ESNet: 8542553
EVO: direct meeting link
Conference Group: 800-377-8846, participant code: 77438230
Slides: talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2009-08 on the JLab CUE (you have to be a member of the "halld" group). This directory is accessible from the web at https://halldweb.jlab.org/talks/2009-08/ .


  1. Minutes from the last meeting
  2. Time-of-Flight Status
  3. Start Counter Status
  4. Action Items


FSU: Chuck Bryant, Sasha Ostrovidov
JLab: Eugene Chudakov, Mark Ito (chair), Sascha Somov, Simon Taylor, Beni Zihlmann


  • Sasha O. told us that Paul Eugenio is on his way to JLab. He is traveling with the FSU engineer and they will be talking to Tim Whitlatch, among others next week.
  • Sasha also told us that an Nathan Sparks, an FSU graduate student, will be working on GlueX, initially doing software (he is also working on CLAS).

Time-of-Flight Work

  • Chuck has done additional measurements; he has started to look at the Hamamasu PMT. He is getting resolution on the time difference between the two end of 124 ps. This compares with 142 ps from the Photonis tube. Note that the Hamamatsu was run at 1700 V, 50 V below the recommended maximum, whereas the Photonis was run at 2300 V, 300 V below nominal. They plan to go back to looking at the Photonis at nominal voltage.
  • Plateau curves show that the right end does not go to 100% as does the left (plateau done with ratio of 4-fold coincidence to 3-fold concidence (2-ends of the counter, 2 trigger scintillators). This was seen with both the Hamamatsu and Photonis tubes.
  • The trapezoidal light guides were used in all of these tests. The final design fishtail will not fit in the dark box.

Start Counter

Sascha S. reported on a meeting with Werner Boeglin, shortly after the BCAL review.

  • Werner submitted a new version of geometry where the bend started more upstream, shortening the barrel section. We also looked at Chuck's drawings. We need to reconcile the geometry in the Monte Carlo with Chuck's drawings and with the Target Group's nominal design. Mark agreed to look at this.
  • SiPM's are a possibility for read-out. They avoid the long light guides needed with the fine-mesh PMT's (about 1.4 m long).
  • We need to understand any mechanical/support with both read-out schemes.
  • Werner is planning measurements from prototypes this month.
  • Sascha thought that another round of dose estimates is needed. There might be background from the collimator cave.

Action Items

  • Reconcile target are geometry version: Mark
  • Further tests on prototype: Sasha O. and Chuck