[Halld-pid] Start counter Meeting Minutes. June 12, 2014

[Mark Ito]

Colleagues,

Please find the minutes below and at 
https://halldweb1.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_June_12,_2014#Minutes 
.

   -- Mark
____________________________

GlueX Start Counter Meeting, June 12, 2014
Minutes

      * FIU: Werner Boeglin, Eric Pooser
      * JLab: Eugene Chudakov, Chuck Hutton, Mark Ito (chair), Bruce
        Lenzer, Tim Whitlatch, Beni Zihlmann

Review of Minutes from Previous Meeting

    We reviewed the [21]minutes from the May 29th meeting.
      * Eric reported that Nick Sandoval has all the cables and the MPOD
        crated and ready to ship. Nick is still doing the individual MPPC
        tests with the laser, masking non-participating MPPCs.

Detector Construction Status

    Eric reviewed a problem with the polishing on the edges of the
    scintillator.
      * Looking at the edges with wrapping. The protective film might have
        messed up view. It was removed on 17 of the counters.
      * He saw buffing scratches in the same location on all counters
      * Some chips on the edges, although there were also some of these on
        the prototypes.
      * Polishing was not done on tip in some cases.
      * He shined a laser into the counters and looked with UV light for
        bubbles.
           + no crazing
           + no bubbles
           + all defects on edges
      * The light tack adhesive was not removed at FIU on those beyond the
        first 17.
      * The scintillator was returned to McNeal for polishing of the edges.
      * Bruce contacted the company to discuss our concerns with their
        process.
      * The counters arrived back yesterday, and visual inspection of the
        first few show good edge surface quality.
      * Tim mentioned that we should add a note about the polishing to the
        mechanical drawings.
      * Initial tests of the scintillators at the SiPM end show time
        resolution 75 to 100 ps worse than seen before. The suspicion is
        that in the studying light transmission across the air gap with
        various configurations the surface of the SiPM go damaged. Eric has
        shipped the SiPM board back to Nick Sandoval. Nick will have a look
        and send back an up-to-date version of the board as a replacement.
        Testing is thus on hold for a few days.
      * The assembly jig is all ready to go apart from the support
        structure.

    [Added in press] Further inspection of the scintillators shows area of
    scratches in two locations on many of the scintillators that were not
    there before they were returned for edge polishing. In addition, Eric
    was told that McNeal had done cleaning of the wide surfaces with a
    commercial glass cleaner in order to remove buffing compound. We will
    meet tomorrow (Friday) to discuss implications.

Support Structure Status

    Tim and Chuck reported that the support structure is complete. It is in
    the Survey and Alignment Lab to check dimensions and configuration. The
    shipping case is ready; care was taken to minimize the possibility of
    damage en route. It should ship to FIU early next week.

Readiness Review

    We discussed what is expected for the review. Bruce will draw up a
    charge to the committee and send that to Werner. We decided on July 8
    as a target date.

Software Status

      * Eric has been working on developing the method for time-walk
        corrections for the past few weeks. It may be that we will need
        different constants for the different regions of the counter:
        straight, bend, and nose. He is getting time resolution using a
        leading-edge discriminator within 10 to 15 ns of that obtained with
        a constant-fraction discriminator.
      * Werner thought that the geometry currently in HDDS is very close to
        correct. He has code to generate HDDS from understood parameters.
        He will look into this area.
      * The start counter is currently being used in the reconstruction.
      * Mark spoke to Hovanes Egiyan about plans for bias voltage control.
        A GUI will be available in August.

Light Tightening the Start Counter

    We discussed several ideas.
      * black tape or Tedlar against the edges of the electronic boards
      * plastic ring on the outside of the boards
      * silicon caulk to fill vulnerable spaces

    This is likely not an insurmountable problem, but requires more
    thinking and discussion.
References

   21. 
https://halldweb1.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_May_29,_2014#Minutes

-- 
Mark M. Ito, Jefferson Lab, marki at jlab.org, (757)269-5295