GlueX Start Counter Meeting, January 27, 2011

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Location, Time

Thursday, January 27, 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
  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, Eric Pooser
  • JLab: Eugene Chudakov, Mark Ito (chair), Sascha Somov, Simon Taylor, Beni Zihlmann

Wrapping Material

The ESR sheets from FSU have still not arrived.

Materials and Construction

  • Lei reports a price of $190 a piece for the scintillator from Elgin. They will have with diamond milled edges.
  • The pieces will be sent to Plastic Craft for cutting, bending, and polishing.

Neutrons and SiPM Damage Rates

Sasha recommended that we look at Richard's recent note on the effect of SiPM dark current on the microscope counters. Some points from that note:

  • Timing resolution is not much affected by dark rate.
  • Looked at rates up to a gigahertz.
  • Photonique devices with a slow recovery rate gives fluctuation in timing resolution due to non-constant exposure to beam.
  • Hamamatsu devices have a faster recovery rate and a steadier response.

Measurements with the New SiPM

Werner and Eric reported on tests that have done the Hamamatsu SiPM that Carl Zorn sent them comparing its performance with a fine-mesh tube that Werner had on hand.

Timing resolution for the SiPM was a bit disappointing. Tests were done with a new scintillator bar from Elgin. The measurements were done with a Sr90 source where the timing was done between the test counter and a trigger counter. Using the PMT, light output and attenuation length measurements were done and repeated with the SiPM. It appears that even with the same amount of light, the resolution for the SiPM is a factor of 1.5 to 2 worse than for the FM-PMT. See [Eric's plots] for details. More study is under-way.

Some other remarks:

  • Pulses generated with an led worked well with the SiPM.
  • They cannot see the single p.e. peak; pedestal is too wide.
  • For the SiPM, there is a 50 mV-ish signal, amplified to 200 mV-ish before being discriminated. The PMT set-up uses the direct signal.
  • They played a bit with bias voltage, nominally 71 V.
  • They are using a constant-fraction discriminator.

Werner also mentioned that if a spare Peltier junction was lying around somewhere, he would be interested in borrowing it.


Mark send Werner a revised version last week incorporation wording that Werner provided. Werner will send a version back with some already-planned modifications to JLab in the near future.