HDGeant4 Meeting, August 11, 2020

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HDGeant4 Meeting
Tuesday, August 11, 2020
3:00 pm EDT
BlueJeans: 968 592 007


  1. Announcements
  2. Review of minutes from the last meeting (all)
  3. Issues on GitHub
  4. Pull Requests on GitHub
  5. Action Item Review


Present: Alex Austregesilo, Sean Dobbs, Mark Ito (chair), Igal Jaegle, Naomi Jarvis, Richard Jones, Mahmoud Kamel, Churamani Paudel, Simon Taylor, Nilanga Wickramaarachchi, Beni Zihlmann

There is a recording of this meeting on the BlueJeans site. Use your JLab credentials to get access.

Review of minutes from the last meeting

We went over the minutes from July 14, a month ago now. Richard has made the judgment that the problem with particle propagation not being able to find the normal to a surface, reported as a warning, occurs rarely enough that it should not cause a problem for us. This we can live with.

Issues on GitHub

We reviewed the issues.

  • hdgeant4 hanging at first event. This problem was introduced in the effort to get reproducible results from all hdgeant4 output events based on the two input random number seeds. The application of mutex locks introduced to use certain ROOT functionality involving the ROOT random number generator had a bug. This is now fixed. Igal will close the issue.
  • G4 exceptions for certain run numbers. We will follow up with Elton on this issue. I may be due to trying to reconstruct TOF-II data with TOF-I-only-compatible software.
  • Difference in Acceptance between G3 and G4. Colin Gleason's last post on this issue showed a large difference in overall event acceptance if simulated with Richard's "no heavy light" branch. The acceptance goes down by a factor of several. We will likely need further guidance from Colin on what particles in the event are creating the difference.

Holes in γγ→η Invariant Mass

Mahmoud showed an anomaly in the two-photon invariant mass distribution near the η. There are dips on either side of the η mass. See his figure below (lower left plot). The dips come from two regions of beam photon energy which are near the corresponding boundaries between the tagger microscope and hodoscope. The regions show as dark blue in the lower right plot. There may some issue with some kind of subtraction from the data since the holes have negative entries in the histogram. Mahmoud will enter this as an issue.

Hdgeant 8 11 2020.png

Added in press: this is now Issue #173.