HDGeant4 Meeting, September 11, 2018

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HDGeant4 Meeting
Tuesday, September 11, 2018
2:00 pm
JLab: CEBAF Center, A110
BlueJeans: 968592007


  1. Review of minutes from last time
  2. Issues on GitHub (all)
  3. New Comparison 4GeV 4 Degree protons



  • FSU: Sean Dobbs
  • JLab: Thomas Britton, Mark Ito (chair), Simon Taylor
  • W&M: Justin Stevens

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

Review of minutes from last time

We reviewed the minutes from August 28.

  • The change to make the time-to-distance relation used in HDG3 match that of data (read it from the CCDB) is in the latest tagged version of halld_sim (3.4.0).
  • Sean reported that the 5 MeV shift in the 2γ mass he reported last time is not limited to just the BCAL or just the FCAL. Both contribute.

Issues on GitHub

We reviewed the extant issues on the GitHub site for HDGeant4. Richard Jones reported (via email) that he is working on the DIRC time propagation anomaly now.

New Comparison: 4 GeV, 4 Degree Protons

Thomas presented plots from a new comparison of 4 GeV, 4 degree protons between HDG3 and HDG4. The comparison was done with all physics processes (multiple scattering, energy loss, delta rays, etc.) turned off.

  • The good agreement after fixes from Richard for 4 GeV protons at 15 degrees, seen after the last round of fixes, stays good in this comparison.
  • The disagreement at 4 degrees persists. It is seen in the following plots:
    • Tracking FOM, wire-based
    • Tracking FOM
  • Thomas will work on getting more detailed plots looking at timing distributions.
  • Events have not been scanned, as was done in the previous round of corrections.
  • HDG3 and HDG4 get their geometry in different ways, with the HDG3 geometry written into auto-generated Fortran code and HDG4 getting it dynamically at run time. We need to check that both are using the same geometry for this comparison. That could explain the difference between 4 and 15 degrees (or not).
  • Thomas will create a new GitHub issue based on this study. [Added in press: see Issue #66]