JEF meeting, August 21, 2020

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Meeting time and location= 9:30 am EST (JLab time) Bluejeans only

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  • SICCAS crystals
    • PS test setup
Colored crystals installed in the PS setup
Comparison of light yield of colored crystals


Attendees: Igal, Arshak, Varun, Jared, Phil, Zisis, Jon, Sasha, Tim W., Jane Josh, Tim B., S.T.

  • Sasha and Josh had previously installed 9 "good" crystals in the PS setup in Hall-D to study light yields.
    • Choose 1 as a reference for light yield comparisons to study "bad" crystals
    • Swapped out 6 crystals, installed crystals showing various levels of discoloration (yellow, brown,...)
    • Discolored crystals show notable degradation in light yield and energy resolution.
      • The worst 2 have 25% worse amplitude and would be rejected (Sasha suggested a 20% threshold w.r.t. nominal "good" crystals)
      • One crystal is right at the border (-20% amplitude) for being rejected: S.T. asked whether it was worth trying to cure this one; Sasha will consider
    • Next plan to install crystals that appear to have bubbles or other internal imperfections
    • Also plan to install Crytur crystals (expected to be better than SICCAS crystals, plan to use as real reference crystals)
  • New light guides: quality better than previous vendor; some evidence for machine marks, could do with better polishing, but satisfactory for what we need
  • PMT divider redesign: slow progress, would help if had face-to-face between Vlad P. and Sasha
    • Plan to install revised version in COMCAL; had hoped to do before TAC run (very soon, if beam comes back!)
    • Sasha would like to test linearity, will need to coordinate with GlueX run coordinator
  • PMT/divider testing - Phil indicated interest in working on this.
  • Igal continued studies of η→π0γγ channel and 3π0 background
    • Optimization of selection criteria
    • Switched to using DReactionFilter with kinematic fitter: χ^2 is most powerful cut
    • Noticed that there was not a huge difference in signal purity between FCAL and FCAL-2 after cut optimization, although resolution got better with FCAL-2
    • Question about shower threshold: S.T. indicated that it is currently the same for both FCAL lead glass blocks and insert
    • Question about covariance matrix: S. T. implemented a diagonal matrix in the code for insert based on Sasha's measurements
      • There is a plan to redo exercise to determine covariance matrix for FCAL, will try to learn how to do this for FCAL-2
  • Jon looked at FCAL-2 efficiency with MC with material in front of FCAL-2 turned off -- efficiency looks flat at ~99% above 2 degrees
    • Indicates features in previous plot due to FDC chambers and other sources of material upstream of the FCAL
  • Liping has completed a draft of our contribution to the Snowmass effort.