[Halld-offline] HDGeant4 Meeting Minutes, June 2, 2020

[Mark Ito]

Folks,

Please find the minutes here 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_June_2,_2020#Minutes> 
and below.

   -- Mark


    HDGeant4 Meeting, June 2, 2020, Minutes

Present: Alex Austregesilo, Sean Dobbs, Colin Gleason, Mark Ito (chair), 
Igal Jaegle, Naomi Jarvis, Richard Jones, Susan Schadmand, Justin 
Stevens, Simon Taylor, Nilanga Wickramaarachchi, Beni Zihlmann

There is a recording of this meeting <https://bluejeans.com/s/9Vixr/> on 
the BlueJeans site. Use your JLab credentials to get access.


      Review of minutes from the last Meeting

We went over the minutes from May 19 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_May_19,_2020#Minutes> 
without much discussion.


      Issues on GitHub

We reviewed some of the issues 
<https://github.com/JeffersonLab/HDGeant4/issues>.

  * Issue #152 <https://github.com/JeffersonLab/HDGeant4/issues/152>:
    BCAL Photon Gun Updates. Mark Dalton posted a new single photon gun
    study for the BCAL. He sees good agreement between G3/HADR1,
    G3/HADR4, and G4. Sean will close this one.
  * Issue #149 <https://github.com/JeffersonLab/HDGeant4/issues/149>:
    BCAL structure in E/p distributions for kaons. This is the issue
    through which we discovered the problem with using the CUTS card.
    Mark will ask Peter Pauli to close this one.
  * Issue #143 <https://github.com/JeffersonLab/HDGeant4/issues/143>:
    BCAL reconstructed energy sometimes broken on startup: multicore
    only. Sean has been able to reproduce the problem with the particle
    gun. Igal also reported seeing the problem when running a single π^0
    particle gun. Richard will look into this one again.
  * Issue #111 <https://github.com/JeffersonLab/HDGeant4/issues/111>:
    Difference in Acceptance between G3 and G4. We reviewed the plot
    Colin posted since the last meeting showing comparisons of timing
    for various particle types in the BCAL and FCAL. The comparison for
    π^− s looks to have a significant contamination from protons. Colin
    is going to pursue a systematic study of these quantities as a
    function of momentum. He will also discuss with Richard a custom
    branch of hdgeant4 that does not register energy in the BCAL for low
    energy neutrons and alpha particles.
  * Issue #93 <https://github.com/JeffersonLab/HDGeant4/issues/93>:
    Calorimeter timing mismatch between g3 and g4. We decided that the
    problems first raised in this issue are essentially the same as
    those being dealt with in Issue #111 (mentioned above). We decided
    to mark this one closed and refer to #111 as a continuation of
    exploration of this issue.


      Bethe-Heitler Generator in HDGeant4

Richard has added his Bethe-Heitler event generator directly into 
HDGeant4 so that events that reflect the coherent bremsstrahlung beam, 
including polarization effects, can be simulated. He has taken care with 
execution efficiency, insuring that events occur in the liquid hydrogen 
target and including adaptive importance sampling of the phase space for 
the QED reaction. He has written a HOWTO 
<https://halldweb.jlab.org/wiki/index.php/HOWTO_generate_Bethe-Heitler_pairs_in_the_GlueX_target> 
on how to run the new generator.


      Event Vertex Simulation

Alex initiated a discussion of Pull Request #156 
<https://github.com/JeffersonLab/HDGeant4/pull/156>: add beam_spot 
center to the printout at initialization. On that pull request, he 
reported inconsistent results when intentionally moving the event vertex 
position in the x-y plane for a simulation and plotting the resulting 
beam spot after reconstruction. The beam spot appeared to move back to 
(0, 0). This pointed to a bug in the tracking where the final step of 
translating coordinates from a reference frame with the origin at the 
(possibly shifted) beam spot back to the global coordinate system was 
skipped. See halld_recon Issue #381 
<https://github.com/JeffersonLab/halld_recon/issues/381>. This has 
likely affected some of our reconstructed data.

The beam position in the x-y plane is retrieved from the CCDB with the 
current VERTEX card scheme. Alex noted that vertex positions are also 
obtained during reconstruction launches of the data. It is not clear 
which determination to use or if even if there is enough difference 
between them to matter. We briefly discussed ideas on how to deal with 
the situation. It will require some more discussion.


      Action Item Review

 1. Ask Peter Pauli to close Issue #149 (Mark)
 2. Study timing in the FCAL and BCAL as a function of momentum. (Colin)
 3. Create a custom branch of hdgeant4 that does ignores energy from
    low-energy neutrons and alphas. (Colin, Richard)
 4. Close Issue #93 and reference Issue #111 as a continuation of the
    work. (Mark, Alex)
 5. Discuss a scheme for setting the event vertex position in the x-y
    plane in simulation. (all)

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