GlueX Start Counter Meeting, November 15, 2012

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GlueX Start Counter Meeting
Thursday, November 15, 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: Thickness studies
  6. Contract

Communication Information

Video Conferencing


Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2012-4Q on the JLab CUE. This directory is accessible from the web at .



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

SiPM Gain Measurement

Eric has done a single photo-electron measurement on a tube to determine its gain as a precursor to measuring the SiPM gain. Fernando Barbosa is waiting on this measurement to finalize his design.

Scintillator Quality

After about a month, the scintillator bars (those that were not broken) are showing visible signs of deterioration, with crazing on many areas of the surface. FIU showed photos of bars illuminated from one end by a diffuse laser light source. Loss of light is clearly seen.

laser test
laser test, close-up

Werner has been in contact with McNeal about their handling practices. Recall that instructions on how to properly handle scintillator had been sent the the company and they claim that those procedures were followed. Yet some samples of the same scintillator material retained at FIU do not show any degradation.

FIU will go ahead and test the bars in any case. They are considering how to proceed. The quality of the machining done at McNeal is fine. The question is whether or not the material handling problem can be solved.

Light Yield Studies

Puneet showed further studies of light collection efficiency. He has improved the geometry to insure adequate coverage of the "detector" regardless of scintillator dimensions. He also can vary the intensity of the source so that it scales with path length and is physically spread along a "track" in the scintillator.

Lately he has been looking at the dependence of the light collection efficiency on the thickness of the counter when the roughness of the edges is greater than that of the faces, as we expect it is in the real counters. With a constant number of photons from the source he hees no dependence on thickness. Studies continue.

Equipment Difficulties

The LeCroy 1454 high voltage mainframe that FUI has been using for PMTs has died. They now only have the capability, using other means, of running a couple of channels. A full cosmic ray run requires six tubes in thier set-up. They do have a CAEN SY2527 mainframe, but the only cards they have on hand are for wire chambers.

We will all explore options for getting them going again.


Mark submitted the purchase requisition for start counter construction to JLab Procurement yesterday. We have to get started on the proposal next.