GlueX Start Counter Meeting, March 6, 2014

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GlueX Start Counter Meeting
Thursday, March 6, 2014
10:00 am EST
JLab: CEBAF Center F326


  1. Announcements
  2. Review minutes from previous meeting
  3. Counter construction status
  4. Support structure construction status
    1. Geometry review meeting re-cap
  5. Electronics status
  6. Lenzer visit to Eljen
    1. Charge to committee
    2. Checklist
    3. accompanying physicist?

Communication Information

Video Conferencing

  • ESNet: 8542554
  • SeeVogh
    • Direct meeting link
    • Phone Bridge ID: 100 2777


  1. Dial
  2. enter access code followed by the # sign: 1833622#

Desktop Sharing

  1. Go to
  2. In the "join a meeting" box enter the Hall D code: 1833622
  3. Fill in the participant registration form.


Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2014-1Q on the JLab CUE. This directory is accessible from the web at .



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

Find a recording of this meeting here.

Review of Minutes from the Previous Meeting

We reviewed the minutes of the February 6th meeting.

  • The Rohacell for the support structure has come in.
  • A draft of the TDR contribution went out. Mark has some comments that he will send to Eric.

Lenzer visit to Eljen

We discussed the charge to the committee (Bruce, Werner, Eric, Mark) and the QA checklist that Bruce has produced.

We also discussed sending another physicist to Eljen to accompany Bruce. Feelings were not strong on this, but we generally thought that Bruce would do fine on his own. We noted that there will be a conference call with Chuck Hurlbut.

Counter Construction Status

Eric gave the report.

Eljen has shipped a single prototype counter to McNeal. The QA guy at McNeal reports that the scintillator is nominal and that machining should be no problem. There was no report on the physical appearance of the scintillator, but this is the same guy who reported the bubbles and he didn't say anything on this aspect.

There have been some minor modifications to the test stand.

Eric has done a scan of the y-position of the scintillator with respect to the SiPM. Results are still being analyzed.

He has also started work on the Monte Carlo, looking to extract the path of charged tracks through the start counter. This information will be needed to get the time-walk corrections.

Support structure construction status

We discussed whether we need to make allowances for wrapping and manufacturing tolerances in the mechanical design. We had an ad hoc meeting on the same subject on February 7. Chuck, Eric, Mark, and Tim were present. If these effects are significant then that will increase the radius of the array. For example, if we need to account for 400 microns of separation between the counters, then the radial position of the counters is displaced 2 mm. Since the sensitive area of the SiPMs is 3&\times;3 mm, this would need to be accounted for.

We discussed various of ways of assigning a reasonable tolerance. If too much is assigned, then there will be over-large gaps between the scintillators; if not enough, the scintillators will not line up with the SiPMs.

Werner pointed out that you could have a lightly greater radius of the array at the upstream end where the SiPMs are and a slightly smaller radius at the downstream end where the acceptance is more important. That takes pressure off of alignment upstream and closes gaps downstream. This could be introduced by a very small bend and/or shimming.

Chuck will work on an set of options in the mechanical model. He will also look into the feasibility of Rohacell shims. FIU will make some additional measurements on prototypes to characterize size variations.

The support ring and inner Rohacell support have not been machined yet, but we have to make a decision soon. We will exchange emails next week on this issue.

Electronics Status

Mark received a report from Fernando Barbosa:

We will start a final round of tests next week. We are also waiting for the aluminum ring to get fit the boards. It would be nice to know when as we will need it in two weeks.

Action Items

  1. Send comments on TDR to Eric. -> all
  2. Incorporate tolerances in the mechanical model.
  3. Take additional measurements of the prototype counters at FIU.