GlueX Start Counter Meeting, July 28, 2011

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Location, Time

Thursday, July 28, 2011
3:30 pm EDT
JLab: CEBAF Center, Room F326/7


  1. Announcements
  2. Review minutes from previous meeting: all
  3. Start Counter News
  4. MOU status

Communication Information


To connect by telephone:

  1. dial:
  2. enter access code followed by the # sign: 3421244#

Video Conferencing


Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2011-3Q on the JLab CUE. This directory is accessible from the web at . You have to be a member of the "halld" Unix group to do this.



  • FIU: Werner Boeglin, Lei Guo, Eric Pooser
  • JLab: Eugene Chudakov, Mark Ito (chair), Puneet Khetarpal, Sascha Somov, Simon Taylor, Tim Whitlatch, Beni Zihlmann

Prototype Status

  • The dark box is in operation.
  • Current set-up uses the 140 cm solid light guide.
    • Previous tests showed a loss of a factor of two in time resolution when using the light guide vs. placing the phototube at the scintillator. That counter was 6mm x 10 mm.
    • Tests were done with and without reflective wrapping material.
    • Using optical grease helped; degradation was only a factor of 1.5.
  • Scintillator from Plastic Craft has been tested.
    • By eye, the quality is not so great. There are scratches and some look milky.
    • Tried test with the piece (of five) that looked the worse.
    • With a FM-PMT directly on the scintillator got 300-400 ps resolution in the flat section and most of the tapered section, but see 600 ps at the forward point.
    • Judging from the previous tests, expect that with the light guide we will see a resolution range of 600 ps to 1 ns.
    • Light output may be improved by improving surface quality of the counters.
    • Want to measure all 5 counters to see if response if uniform
    • Vapor polishing looks like promising option.
  • Setting up to test fiber light guide
    • A new mounting scheme has been built.
    • These should have better light transmission.


Tim emphasized the need to have a good idea of the start counter geometry and support scheme now design of the target is progressing. One design cannot proceed without knowledge of the other.

Werner will send Tim the drawing of the current design. The Plastic Craft pieces conform to this design.

Fiber Start Counter?

Beni described ideas that have been discussed at JLab about using the excess fibers from BCAL reconstruction to build a start counter. There was a lot of discussion of possible design ideas. Werner pointed out that this idea was considered some years ago. The principal issue is how to transitions the fibers from the barrel section to the "nose cone" section or whether a nose cone is needed at all. Also raised was the idea that a more complicated design might be more appropriate for an upgrade. More discussion and some preliminary drawings are needed.

SiPM option

Fernando Barbosa has recently reported tests with a new version of the pre-amp for the BCAL SiPM arrays that appears to give sub nanosecond intrinsic rise time. Werner has not been pursuing the SiPM option recently due to the disappointing results from tests last year. The device he tested before had a rise time of 20 to 22 ns. If there is a new device available with markedly better performance then he is interested in repeating some of those tests.


The MOU is going around university administration at FIU for signatures.