HDGeant4 Meeting, February 26, 2019

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HDGeant4 Meeting
Tuesday, February 26, 2019
3:00 pm
JLab: CEBAF Center, A110
BlueJeans: 968592007


  1. Review of minutes from the last HDGeant4
  2. Review of discussion at Collaboration Meeting
  3. Do-over on comparison studies
  4. Peter's comparative study of HDG3 vs. HDG4
  5. G3/G4 Comparison for ρ(770) cross section (Alex):
    • Acceptance
    • Full Comparison with biggest offenders (pages):
      • FDC Cathode (32, 54)
      • StartCounter (290, 412++)
      • BCal (77, 252, 316)
      • FCal (287, 373)
      • Protons (526++, 976)
      • Pions (1028++)
      • Beam Photons (639)
      • Vertex time (113), Track timing (872++)
  6. Written Report (outline)
  7. Issues on GitHub (all)
  8. Pull Requests on GitHub (all)



  • CMU: Naomi Jarvis
  • JLab: Alex Austregesilo, Thomas Britton, Sean Dobbs, Stuart Fegan, Mark Ito (chair), Dmitry Romanov, Simon Taylor, Beni Zihlmann
  • UConn: Richard Jones
  • W&M: Justin Stevens

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

Review of minutes from the last HDGeant4

We went over the minutes of the February 12 meeting. Mark reported that there is still no version set using the HDDS 3.14, the release with pre-DIRC geometry baked in.

Do-over on comparison studies

Simon is working on a set of studies using the particle gun, with all the physics of particle interaction with matter turned on. He will report on it at a future meeting.

Peter's comparative study of HDG3 vs. HDG4

Thomas led us through Peter Pauli's slides on a comparative study of pKK in both Monte Carlo and data. Several slides showed comparisons of histograms from four points of view:

  1. as generated
  2. as reconstructed after simulation with hdgeant
  3. as reconstructed after simulation with hdgeant4
  4. real data

In many cases the hdgeant4 results looks a lot more like data. Note that it is unlikely that the generated distributions are the same as occur in the real world (as Matt pointed out at the collaboration meeting), but often the better agreement of data with hdgeant4 is due to a lack of sharp features seen in the hdgeant simulation and not in any of the other distributions. Also the fits to SDME's look a lot better when using hdgeant4 than with use of hdgeant. Peter concluded that he needs to use hdgeant4 for his work.

G3/G4 Comparison for ρ(770) cross section

Alex showed his recent comparative analysis of the low-energy ρ data.

First he showed a plot comparing acceptance as a function of energy. He gets differences between G3 and G4 at lower beam photon energy in constrast to results from Peter and Simon.

He then showed highlights from comparisons of monitoring histograms, with the results of G3 and G4 overlayed on a single histogram. He used a macro from Sean to do this. There are 1,277 such plots in total. Here are the items he bookmarked:

  • FDC Cathode (32, 54)
  • StartCounter (290, 412++)
  • BCal (77, 252, 316)
  • FCal (287, 373)
  • Protons (526++, 976)
  • Pions (1028++)
  • Beam Photons (639)
  • Vertex time (113), Track timing (872++)

There was some question about whether the HDG3 results used the pre-DIRC geometry. Alex and Thomas will check on this a re-run the simulation if necessary. Two features stood out:

  1. The start counter is missing its complement of recoil protons at 60 degrees in polar angle. Alex will submit an issue; Richard will investigate.
  2. The effect of the trigger for low-energy beam photons, seen in HDG3 is absent in HDG4. This could be due to differences in the way charged hadrons are treated in the FCAL. Differences in FCAL energy are seen in the relevant plots which go in the right direction (more energy for HDG4). More investigation is needed.

Written Report

Mark proposed an outline for a written report from this committee describing the work we have done and recording our recommendations. There were no strenuous objections to going in the direction indicated.

Issues on GitHub

We looked at Issue #89: Hit Energy Agreement, submitted earlier in the day by Rebecca Barsotti. Richard summarized his explanation of why differences in shower energy are not surprising when comparing HDG3 and HDG4.