May 10, 2019 - PrimEx-Eta Meeting

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Time and Place

  • Time: Friday, May 10, 2019 2:00 pm EST.
  • Room: CEBAF Center, Room F227

Meeting Connections

  1. If joining via web browser, go to [1]
  2. If joining via phone, use one of the following numbers and the Conference ID: 7572695553.
    • US or Canada: +1 408 740 7256 or
    • US or Canada: +1 888 240 2560
  3. If joining via Polycom room system go to the IP Address: ( and enter the meeting ID: 7572695553.


eta -> yy Cuts and Veto Plots


  1. eta -> 2gamma Plots
    • Drew showed some plots (see slides) showing the motivations for the cuts and vetos used in selecting eta -> 2gamma events, as well as highlighting some issues that will need to be studied in detail at a later point.
    • These plots were all made using the default calibration constants with a time stamp from the middle of April, so they don't have any updates to the timing or energy calibrations applied.
    • It would good to ask Sean to attend one of the meetings in the future to give a detailed explanation as to how the fcal and rf timing is calculated.
    • Ilya pointed out that we will likely need to study each channel of the hadronic background individually with simulations.
    • For some reason, subtracting accidentals reduced the eta yields consistently over all angular bins. This likely indicates an issue with the fitting that needs to be corrected.
  2. CCAL LED stability
    • Sasha showed some plots of the LED signal amplitude as a function of the run number.
    • His plots showed the signals were pretty consistent (2-3% fluctuations), however some channels close to the center saw a clear trend in the signal amplitude over the course of the run
    • Reference PMT signals also look pretty stable, with even less fluctuation.
  3. Overview of Ilya's physics talk at the collaboration meeting:
    • what is primexd, statistics
    • mention compton on different targets
    • dNdTheta, constrained mass, elasticity
    • Future Plans:
      • analyze data
      • ask for second run