Time-of-Flight/Start-Counter/Target Meeting, November 13, 2009

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Location, Time

Friday, November 13, 2009
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/2009-11 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/2009-11/ .


  1. Minutes from the last meeting
  2. Time-of-Flight Status
  3. Start Counter Status
  4. Target Status
  5. Action Items


FIU: Werner Boeglin
FSU: Sasha Ostrovidov
JLab: David Lawrence, Mark Ito (chair), Sascha Somov, Aram Teymurazyan
UMass: Rory Miskimen

Time-of-Flight Status

Sasha O. gave us an update:

  • The cross-talk problem reported at the last meeting has been reduced to a few percent of the neighboring channel pulses. Many things were checked; the identity of the magic bullet is not known.
  • A 4 ns delay cable is being used on the Phillips discrimintor as suggested by Beni Zihlmann.
  • With the new set-up he is seeing 100 ps resolution on the time difference. This is to be compared with the 124 ns he saw with the CAEN VME discriminator.
  • He is now running cosmic tests with an Ortec CF8000 discriminator.
  • No time walk corrections have been applied to any of the tests so far.
  • Sascha S. raised the possibility that rate considerations might argue for leading-edge discriminators. David pointed out that with a time-walk corrections, the leading-edge discriminator might do as well in offline reconstruction as a constant-fraction model.
  • Sasha O. is still hoping to get a flash ADC from JLab.

Start Counter Status

Werner started to report on light output studies he has been doing, but most of his report had to be postponed due to technical audio difficulties of unknown origin. Mark and Werner will investigate.

Mark recapped some notes from a conversation with Sascha S. about start counter geometry:

  • Werner has a python (perl?) script that generates an HDDS specification of the start counter, including rohacell support and light guides. Seem like this works, more or less.
  • Tim/Chuck have some version from the past that has an uncertain relationship to the latest design.
  • The version in HDGeant presently is pretty close to Werner’s latest thinking.
  • Essential features of the current design are 40 sectors, 2 cm diameter opening for beam in forward direction.
  • Need a way to align HDGeant and Tim’s/Chuck’s (I-deas) drawings
  • Need to establish an authority for changing the geometry of the target. Some start counter design considerations might depend on the possibility of changing target geometry choices.

Probably the easiest way to keep things in alignment would be if Werner could interface with both Tim/Chuck (on the I-deas side) and Sascha S. (on the HDDS side).

Target Status

Rory oriented us on how the target effort will be organized. He had just had a meeting yesterday with Eugene Chudakov, Elton Smith, and Aram.

  • The target will remain principally a JLab project, taking advantage of the cryogenic expertise of the Lab's Target Group.
  • UMass will play a significant role in organization and oversight.
  • UMass will also participate in the related slow controls, though that role has not been defined yet.
  • Solid targets will also likely hold interest for the main GlueX program, especially for calibration and commisioning.
    • The default idea is to physically remove the cryotarget, and insert some kind of target ladder
    • Keeing the solid target structure permanently downstream of the cryotarget is not attractcive for GlueX because of the extra material in the beamline. (This was discussed last Spring.)
    • change-over time should be about eight hours.
    • UMass would build the ladder for the solid target
    • The roster of target materials is yet to be decided. Input from GlueX collaborators is welcome, especially if certain materials/configurations would be more useful for calibration purposes.
    • If cryotarget comes out, there is room for flexibility in the mechanical design.
      • perhaps a target wheel
      • perhaps motion in z
      • perhaps a single foil at detector center
  • Rory wondered how much of the standard GlueX programs depends on cross section measurements, i. e., how precisely does the target thickness need to be known.
  • An MOU is being prepared between UMass and and the Lab on this effort.
  • Cryotarget design and fabrication:
    • JLab Target group will make the target, cryogenic system.
    • Target cells will be made in a Steve-Christo-like fashion.
    • We may buy a stand-alone refrigerator, decoupled from the magnet cryosystem.
    • PrimEx may require a wider target cell than GlueX requires so that most photons from eta decay will exit the target through the downstream window.