Time-of-Flight/Start-Counter/Target Meeting, January 8, 2010

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Location, Time

Friday, January 8, 2010
2:00 pm EDT
JLab: CEBAF Center, Room F326/7
ESNet: 8542553
EVO: direct meeting link
Conference Group: 800-377-8846, participant code: 77438230
Slides: talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2010-01 on the JLab CUE (you have to be a member of the "halld" group). This directory is accessible from the web at https://halldweb.jlab.org/talks/2010-01/ .


  1. Minutes from the last meeting
  2. Time-of-Flight Status: Sasha O.?
  3. Start Counter Status: Werner? http://markito3.wordpress.com/2009/09/18/targetstart-counter-geometry/
  4. Target Status: Aram?
  5. Action Items


FIU: Werner Boeglin
JLab: Chuck Hutton, Mark Ito (chair), Sascha Somov, Simon Taylor, Elliott Wolin

Minutes from the last meeting

We went over them. Elliott talked to Chris about controls. Chris's concern about programming PLC's is not an issue.

Start Counter status

Sascha showed before and after plots of a radiation scan of the target/start-counter area. These show the amount of material an infinite momentum particle will encounter when launched from the center of the target. Improvement is seen in the start counter component due to a new geometry which starts the bending farther upstream and in the "target" component due to a shortened scattering chamber (end cap moved upstream). See Mark's notes on an old version of Chuck's drawings for a guide to the geometry.

Werner gave us an update:

  • 3 mm scintillator looks OK; seems to give sufficient light
  • 350 ps time resolution has been measured with a fine-mesh phototube
  • He will try tests with the new SiPM from Hamamatsu
  • The SiPM he has in hand has too low a PDE
  • Rise time with the fine-mesh PMT is 2 ns
  • He has tried wrapping the counters with VM2000[?], a highly reflective material. This really helps light yield.
  • He is thinking of a scheme where the wrapping provides optical isolation among the counters, but not necessarily a completely light-tight seal. That could be provided by a global enclosure.
  • He is doing measurements with 2 mm scintillator currently.

Werner will be travelling to JLab on the 21st and will be available to discuss start counter issues.