GlueX Start Counter Meeting, December 20, 2010

From GlueXWiki
Jump to: navigation, search

Location, Time

Monday, December 20, 2010
1:30 pm EST
JLab: CEBAF Center, Room F228


  1. Announcements
  2. Review minutes from previous meeting: all
  3. Start Counter News: Werner
  4. Neutron flux and Start Counter SiPM's: Sascha
  5. Photodetector decision process: all
  6. MOU plans: all


Conference Group, US: 800-377-8846, Canada: 888-276-7715, International: 302-709-8424
   participant code: 77438230
ESNet: 8542553
EVO: direct meeting link, phone bridge ID: 7 7569
Slides: talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2010-12 on the JLab CUE. This directory is accessible from the web at .


  • FIU: Werner Boeglin, Lei Guo
  • JLab: Mark Ito, Sascha Somov

Wrapping material

Paul Eugenio has sent some ESR sheets sent to FIU. They have not been received yet.

Counter Fabrication

Lei has had futher contact with the company that is fabricating light guides for the CLAS12 central TOF.

  • They can do bending for no extra charge.
  • They estimate a failure rate of 3 out of 8.
  • The cost should be a few hundred dollars per counter.
  • One possibility is to buy scintillator in sheets and have the company do the cutting, bending, and polishing.
  • Practice for the company with plexiglass seems the likely next step.

Neutrons and SiPM damage rates

Sasha reviewed the damage estimates on his wiki page.

  • The damage rate is comparable to that of the downstream end of the BCAL.
  • Polyethylene shielding helps. This was studied for the tagger and reduced the damage rate by about a factor of 7.
    • The support structure itself could be made out of shielding material.
  • The start counter is a timing application, not an energy measurement. That should increase its tolerance to dark current.

Further Tests

  • Werner wants to look at new scintillator bars with new SiPM. So far the timing resolution has been dominated by light output.
  • Sascha reported that Richard Jones simulated discriminator response in the microscope with a SiPM with elevated dark rate. He found that the timing resolution was OK with a factor of 50 increase in dark rate. For the microscope he expects 300 pe's total.
  • Werner suggested that we can change dark current with temperature in order to test timing response.
    • We need to ask Carl Zorn how hot does it have to be.
  • Sascha quoted a start counter rate of 12 kHz, versus 1 MHz for the microscope.
  • Werner has a 4x4 array: Hamamatsu F10943.
    • Sascha suggested we ask Carl for another one.
  • Werner is changing his set-up to do light output measurements to accommodate the SiPM as main detector.
  • The new scintillators he plans to use are:
    • 2 mm and 3 mm thick, 12 mm and 15 mm wide
    • The 15 mm wide counters could be used for a 30 element design.
    • Since he observed light output reduced by edges, a wider wider counter has less edge area fractionally.
  • The plan is to focus on the SiPM solution, using the same one as for the BCAL.

Other Items

  • Werner mentioned the possibility of funding the project through an MRI.
  • The light guide design is non-trivial. Although there is a rough match in cross sectional area between the scintillator and SiPM, the aspect ratios are pretty different.