[Halld-offline] HDGeant4 Meeting Minutes, June 29, 2021

[Mark Ito]

Folks,

Please find the minutes here 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_June_29,_2021#Minutes> 
and below.

   -- Mark

      ___________________________________


    HDGeant4 Meeting, June 29, 2021, Minutes

Present: Alex Austregesilo, Tegan Beattie, Sean Dobbs, Mark Ito (chair), 
Richard Jones, Zisis Papandreou, Simon Taylor, Jon Zarling, Beni Zihlmann

There is a recording of this meeting 
<https://bluejeans.com/s/Rho3x4PNH1b/> on the BlueJeans site. Log into 
the BlueJeans site <https://jlab.bluejeans.com> first to gain access 
(use your JLab credentials).


      Review of minutes from the last meeting

We went over the minutes from the meeting on June 15 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_June_15,_2021#Minutes>. 


We discussed what combination of versions we should aim at for the next 
major upgrade. We settled on the following:

  * GCC 8.x
  * ROOT 6.24.x
  * Geant4 10.06.x

The recommended Linux distribution is CentOS 7 with Developer Toolset 8 
<https://www.softwarecollections.org/en/scls/rhscl/devtoolset-8/> (to 
provide GCC 8). A Singularity container with this combination has been 
built.


      Charged hadron timing in the BCAL

Tegan showed his start at looking at charged hadrons in the reaction 
γp→π^− Δ^++ . He has been working with Jon to set up the apparatus up to 
compare simulation with real data. He showed some preliminary plots that 
show good agreement. Notably he sees some double peaks in timing for 
data, probably due to proton/pion mis-identification, and those same 
peaks seem to be there in the simulation as well. See his plots in the 
recording.

Tegan observed that with the good agreement he is seeing between 
simulation and data in single particle studies it becomes even more 
interesting to revisit the original studies of event efficiency that 
started us on this path.


      Comparison of Models of Polarized Bethe-Heitler Production

Richard showed recent work comparing simulated Bethe-Heitler events 
between his Diracxx package and a generator built into a recent version 
of Geant4. He has reason to believe that the "Butler" model in G4 is 
close to that used by Andrew Schick in his simulations, which Andrew got 
from Rory Miskimen. The Butler model ignores the nuclear form factor, 
whereas it is taken into account in the Diracxx-based program. Richard 
sees the expected suppression of the cross section due to the form 
factor at high pair mass, where GlueX has acceptance, by a factor of a 
few compared to Butler. He sees agreement in the analyzing power 
predicted by the two models. He plans on giving a more comprehensive 
description of this work at the next Beamline Working Group meeting.


      Action Items

 1. Re-do comparisons of overall event reconstruction efficiencies.
 2. Think about how to study the Schick-Smith-Dalton effect(s). (all)
 3. Think about a GlueX Doc on simulation. (all)
 4. Think further about how to get to modern versions of external
    software packages. (all)


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