GlueX Start Counter Meeting, March 10, 2011

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Location, Time

Thursday, March 10, 2011
3:30 pm EST
JLab: CEBAF Center, Room F326/7


  1. Announcements
  2. Review minutes from previous meeting: all
  3. Start Counter News: Werner, Lei, Eric
    • Plastic handling company info and costs
  4. MOU plans: all

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/2011-1Q 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
  • JLab: Mark Ito (chair), Sasha Somov

Start Counter News

  • The new scintillators have been shipped to Plastic Craft[?].
  • Werner and Eric have looked at a new fast shaping amplifier. It looks good so far. They will start on a series of measurements tomorrow to see if it helps with time resolution.
  • FIU is interested in pursuing the same detection/read-out scheme that Richard Jones is exploring for the tagger microscope. The idea is to use four independent single-cell 3x3 mm SiPM's rather than the 16-cell array being used for the BCAL. Because of higher capacitance in the array, rise-times are much longer that those expected for single cell devices. The signals out of the individual pre-amps would be summed and the summed signal discriminated [amplified/shaped first?]. If the rise-time can be preserved through this process, better time resolution should result.
  • Sascha will be ordering several of the single-cell devices for testing this idea to supply both the microscope and start counter investigations. There was some detailed discussion of surface mount vs. ceramic types and 25 micron vs. 50 micron technology. The price seems to be in the neighborhood of $200 per device.
  • Werner is also interested in getting advice and/or hardware from JLab for cooling the SiPM's in his test set-up.
  • The current goal for timing resolution is about 350 ps[?]. The results from SiPM's with the prototype counters are in the range 500-600 ps thus far[?]. Mark asked if we could live with a device with poorer resolution than this goal and rely on other detector elements to provide enough time discrimination to pick out the correct RF bucket. Others thought that having the good resolution was important and we should not give up the idea of the start counter independently determining the beam-on-target time.
  • [Added in press.] Mark discussed this issue with Elton after the meeting and he mentioned that CLAS has been able to use its start counter to determine the beam time in just this way and this capability was important in the reconstruction.
  • FIU also plans to pursue the option of using fine-mesh PMT's for the readout. Recall that this requires some sort of light guide so that the tubes can be in a region of sufficiently low magnetic field (a meter or so of light guide).

MOU Status

Mark will review and accept the changes that Werner sent last month and distribute it more widely within the Hall D group for comment.