[Halld-offline] HDGeant4 Meeting Minutes, December 1, 2020

[Mark Ito]

Folks,

Please find the minutes here 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_December_1,_2020#Minutes> 
and below.

   -- Mark

__________________________


    HDGeant4 Meeting, December 1, 2020, Minutes

Present: Alex Austregesilo, Tegan Beattie, Sean Dobbs, Colin Gleason, 
Mark Ito (chair), Igal Jaegle, Naomi Jarvis, Richard Jones, Zisis 
Papandreou, Simon Taylor, Beni Zihlmann

There is a recording of this meeting 
<https://bluejeans.com/s/mQ@IoAghvqn/> on the BlueJeans site. Use your 
JLab credentials to get access.


      Announcements

Mark announced that he has a complete build of CentOS 8 available at 
JLab. It uses the default version set: version_4.32.0.xml.

  * The directories are in the standard place on the group disk:

/group/halld/Software/builds/Linux_CentOS8-x86_64-gcc8.3.1-cntr

  * The build is now getting shipped to Oasis and is available via CVMFS.
  * The corresponding singularity container is in the "dist" directory:

/group/halld/www/halldweb/html/dist/gluex_centos-8.2.2004_sng3.6_gin2.15.sif

and is available for download from

  https://halldweb.jlab.org/dist/gluex_centos-8.2.2004_sng3.6_gin2.15.sif  <https://halldweb.jlab.org/dist/gluex_centos-8.2.2004_sng3.6_gin2.15.sif>

After the announcement we had a discussion on how to transition to GCC 
compilers beyond 4.8.5, the default for CentOS 7. Moving to more 
advanced versions of ROOT and Geant4 depend on making this transition.

  * Mark has been thinking that by going to CentOS 8, either via
    container or actual of the new OS, we get to GCC 8.3.1 a big leap
    forward with an unambiguous prescription for going forward.
  * Richard and Sean advocated keeping at CentOS 7 since, after all, it
    represents the bulk of our installed base, and using DevToolSets
    from Software Collections to get an upgraded GCC.
  * Richard mentioned the use case where a CentOS 7 container is used
    with CVMFS to get the software. Here the OS and built software are
    provided; users in this category don't care how the sausage is made.
  * Sean mentioned the use case where only ROOT files are analyzed using
    gluex_root_analysis. All of the build issues are moot in this case
    as well.
  * Beni pointed out that by going to a new version of the OS, we get
    upgrades on many packages all at once, not just GCC, and eventually
    all of these upgrades will have to be faced. If we follow the new OS
    approach, confronting these problems will give us flexibility and
    save pain down the road.
  * Sean advocated an approach where we specify a minimum compiler
    version as a starting point and work on guidance for every to get
    there.
  * Mark will continue to think about a recommendation for best
    practices. He found the discussion very useful in this regard.


      Review of minutes from the last meeting

We went over the minutes from September 22 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_September_22,_2020#Minutes>. 
Sean mentioned that the details on how to widen the Δt cuts to make 
efficiency calculations more reliable was taken up at the PID meeting 
this morning 
<https://halldweb.jlab.org/wiki/index.php/GlueX_PID_Meeting,_December_1,_2020>. 



      Issues on GitHub

We spent most of the remaining time discussing Issue #111 
<https://github.com/JeffersonLab/HDGeant4/issues/111>, *Difference in 
Acceptance between G3 and G4* Colin lead us through the issue. There was 
a lot of leading to do since he first submitted the issue in May of 2019 
and it has remained active, with many updates over time. [The secretary 
refers the reader to the link above rather than attempt a comprehensive 
summary.]

There followed an active discussion of ideas related to the issue.

  * With respect to the low acceptance in G4 when using the "no heavy
    light" (NHL)branch, Richard suspects that simply turning off energy
    deposition for particles heavier than a proton might be too naive an
    approach. That and the fact that if the energy reported out by the
    Monte Carlo is not the energy deposited by particles in sensitive
    volumes, then there needs to be a calibration step as is done with
    real data. He outlined ideas for adding detail to the energy
    read-out from the Monte Carlo where the details of how much energy
    loss shows up as visible light in the BCAL scintillation fibers. He
    noted how these details are different depending on particle species:
    photons are different from pions, and pions perhaps different from
    protons.
  * Sean emphasized that the main problem with getting efficiency
    calculations to agree with each other is tails on the timing
    distributions for charged hadrons in the BCAL, rather than the
    overall energy response, although the two issues could easily have a
    common cause.
  * Alex reminded us that in his study of pion timing from rho events,
    he tried various time windows, going all the way to ±5$nbsp;ns,
    and even there he saw differences in efficiency between the
    different hadronic interaction models.
  * Colin had two suggestions for further studies.
     1. Rather than looking as the relatively complicated topology of
        γp→ηπ^− Δ^++ , we drop back to a single particle gun study
        inspired by differences seen in the full reaction.
     2. On and event-by-event basis, study where the cuts differ when
        using different hadronic interaction models for the same event.
  * Richard also had suggestions on what to try next:
     1. Look at the timing distributions for charged hadrons in the BCAL
        on the NHL branch. If the high side tail that we have been
        discussing is due to late neutrons and/or decaying nuclear
        fragments as he suspects, then it should absent when using this
        branch.
     2. Look at the effect of the NHL branch on photon energy and if it
        is present, measure the energy deficit and use that measurement
        to apply a correction to the reconstructed photon energy. Once
        that is done, look at the effect on overall event efficiency,
        again using the NHL branch, on Colin's reaction.
  * Sean reminded us of a talk that Mark Dalton gave at a GlueX workshop
    <https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=4053>
    in May 2019. Mark showed a variety of effects in data and Monte
    Carlo. Sean showed the slide on BCAL timing resolution as a function
    of energy and BCAL shower time offsets as a function of both energy
    and z-coordinate. There are many features that we still do not
    understand in detail. Sean does not want us to lose track of these
    issues.
  * Zisis reminded us that Andrei Semenov developed a detailed Geant4
    simulation of the BCAL with the geometry of the fibers and lead
    sheets expressed explicitly. This may come in handy as we focus in
    on details.
  * The group thanked Zisis for getting the group fired up to re-address
    these issues and also welcomed Tegan to the effort.


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