GlueX Start Counter Meeting, May 28, 2020

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GlueX Start Counter Meeting
Thursday, May 28, 2020
10:00 am EDT
BlueJeans: 556 286 544


  1. Announcements
  2. Review minutes from the last meeting
  3. Calibration and Efficiency
  4. Dark Rate Studies
  5. Action Item Review


Present: Rupesh Dotel, Mark Ito (chair), Susan Schadmand, Simon Taylor, Beni Zihlmann

Review of minutes from the last meeting

We went over the minutes from April 16 without significant comment.

Calibration and Efficiency

Rupesh has measured timing resolutions for several runs (71728, 71785, 71822 71840). All were taken at 350 nA beam current and all used the same set of calibrations constants, those obtained from run ?. The resolution, averaged over all thirty counters shows some slight worsening as time goes on. We discussed whether this might be due to increased dark rate, or gain degradation, or some other effect.

We asked Rupesh to repeat the exercise for a run close to the end of the running period to see if the trend continues. We also asked him to recalculate the calibration constants for one of the run that shows the worsening in resolution to see if there are significant changes.

We could not remember if gain calibrations were done for the Start Counter in the past. Rupesh will look into this.

We also discussed whether we should see recovery of the dark rate of the SiPMs from simply not running for an extended period of time (as we are in now). We need to revisit Yi Qiang's study.

Rupesh also told us that it takes a month on the farm to analyze obtain calibration constants for three run. This seems unacceptably long. We will review procedures offline to see if there are changes that can speed up the process.

Action Item Review

We came up with the following list:

  1. Document calibration procedure (Rupesh)
  2. Reproduce Beni's dark current results. (Tolga)
  3. Measure resolutions for a run near the end of the run just past. (Rupesh)
  4. Repeat the calibration procedure for one of the runs that shows worsened timing resolution. (Rupesh)
  5. Research the existence of gain calibrations. (Rupesh)
  6. Revisit Yi's study of SiPM annealing. (Mark, Beni)
  7. Review the calibration procedure with an eye to speeding them up. (Mark, Beni, Rupesh)
  8. Ask about the current recommendation from SciComp on copying files to the local disk from cache before analyzing them. (Mark)