GlueX Start Counter Meeting, July 26, 2012

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GlueX Start Counter Meeting
Thursday, July 26, 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:
    1. Start Counter Background Studies
    2. Start Counter Simulations
  6. Contract

Communication Information

Video Conferencing


Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2012-3Q on the JLab CUE. This directory is accessible from the web at .



  • FIU: Werner Boeglin, Puneet Khetarpal
  • JLab: Eugene Chudakov, Chuck Hutton, Mark Ito (chair), Sascha Somov, Beni Zihlmann

Prototype News

  • The new scintillator from Eljen has not been ordered yet. The order should go out next week.
  • Werner contacted Elgen and asked about diamond-milled edges
  • Werner has been thinking of an alternate scheme for wrapping the scintillator to eliminate cross-talk. Eljen has a double-sided aluminized mylar, two microns thick total, used for entry windows for alpha detectors to make them light tight. He is thinking we could wrap the entire counter in this material. It has 1000 Angstroms of aluminum on each side.
  • Chuck will send drawings of the individual counters to Werner. These will have the latest dimensions.

Read-Out Design

FIU received the boards from Fernando Barbosa on Monday. They have two one-sector detectors, each with 4 SiPMs, one with 50 micron devices, the other with 100 micron devices. They are about to start testing them. Fernando is interested in the results so he can fix the gain in the design.


Background Studies

Puneet presented rate calculations done with the new start counter geometry (30 counters). See his wiki page for details. He showed overall rates, the spatial distribution of the hits and energy spectra both for electromagnetic background and for hadronic events.

There was some discussion of his results:

  • We need to understand the details of the digitization model.
  • Beni noted that HDGeant applies a threshold cut of 150 keV on hits.
  • HDGeant is assuming an attenuation length of 150 cm. It should be more like 60 cm.

Optical Simulations

Puneet also described progess in modeling the optical response of the counters in Geant4, including different optical properties for different faces of rectangular counters. See his wiki page for details. He find a reduction of the light output for a fixed sized sensor as the thickness of the counter the counter. The source for these studies is a point source of photons positioned at various distances from the sensor.

The next step is to implement these features on the actual bent counter geometry.

Action Items

  1. Send new counter drawings to Werner. -> Chuck
  2. Test the SiPM start counter electronics.
  3. Start work on the SOW. -> Mark, Werner