GlueX TOF Meeting, June 23, 2011

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Location, Time

NOTE: Non-standard room, date, and time!

Thursday, May 23, 2011
11:00 am EDT
JLab: CEBAF Center, Room L207


  1. Announcements
  2. Minutes from the last meeting
  3. Mantis task tracker project for TOF: Mark
  4. Prototype Status [1]
  5. Contract Status
  6. Meeting time



  1. ESNet: 8542553
  2. EVO: EVO site


  1. dial:
  2. enter access code followed by the # sign: 3421244#


Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2011-2Q on the JLab CUE. This directory is accessible from the web at .



  • FSU: Sasha Ostrovidov
  • JLab: Paul Eugenio, Chuck Hutton, Mark Ito, Simon Taylor, Tim Whitlatch, Beni Zihlmann

Minutes from the Last Meeting

We reviewed the minutes from the May 27th meeting.

  • Paul's students are back in Tallahassee after attending HUGS.
  • Mark purchased the raw light guide material as requested by Paul. It has been received at FSU.

Mantis task tracker project for TOF

Mark pointed out that he has created a project to track TOF action items in the Mantis Bug Tracker. Any collaborator can create an account that uses your JLab password and add, modify, or remove entries.

Design and Prototyping


We had a discussion centered around the design drawings enumerated by Paul and reserved in Oce by Chuck. Some of the issues discussed:

  • light guides must be bent to accommodate the diameter of the PMT's with their shielding, what is the best way to do this?
  • how to best support the counter-light-guide-tube-cable assemblies
  • two options for manufacturing the bent light guides
    1. heat and bend the Lucite
    2. machine entire 3-D shape out of single piece of Lucite
  • Paul is looking into the single-piece option.
    • This method requires a 3.5" diameter Lucite rod, unfortunately 3" is the largest "stock" size at McMaster. The price goes up by a factor of 2.5 if a custom size is ordered.
  • We discussed whether UV-transparent Lucite was necessary.
    • Tests with both UVT and non-UVT light guides at FSU gave similar results, as expected.
    • Elton thought that UVT plastic was important for the BCAL; we will have to talk to him about this issue.
  • Paul raised the possibility of using vapor polishing on the machined light guides. He has identified a company that will do a trail piece at no cost.

We will have a meeting in a week, tentatively Thursday, June 30 at 10 am, with engineering and design folks at FSU and JLab to discuss how to proceed with producing drawings. Mark will send an announcement.


Sasha led us through some plots showing results from recent tests at FSU. Quoting from his presentation:

  • Good news: Switch to a leading-edge discriminator (LED) from a constant-fraction discriminator (CFD) has eliminated multiple timing peaks. We confirmed the presence of these peaks with both CAEN 812 VME CFD and Phillips 715 NIM CFD. Peak positions were strongly correlated with the value of internal CFD delays. Apparently, the CFD method of inverting, delaying and subtracting part of the signal does not work well with signals of certain magnitude/shape.
  • Problem: While time differences with the LED do not show extra timing peaks, the shape of the time-difference spectrum when using 2 short trigger paddles is somewhat puzzling, with a dip in the middle rather than at both ends. This results in highly non-Gaussian timing distributions. Time-walk corrections improve overall timing resolution from 180 ps to 115 ps but we hope to improve this number if the shape of distribution is better understood.


We looked at the [schedule (i. e., the APP)]. We have slipped over a month from where we said we will be. Getting the drawings done is the next big step; it will force some decisions.

Paul will write a draft statement of work. The required drawings and specifications will be called out if not detailed. He will send it to Mark who will pass it around for review.

Meeting Time

We decided on regular time for future meetings: bi-weekly, 10 am on Thursdays.

New Action Items

  1. Paul will send Chuck specification for PMT geometry.
  2. Talk to Elton about UVT light guides.
  3. Schedule TOF design meeting for Thu. June 30.
  4. Order 3.5" diameter Lucite rod for light guide machining tests.
  5. Distribute reference on vapor polishing.
  6. Find out if PMT's need specification in FSU contract if they are being bought by JLab.