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<p>Folks,</p>
<p>Please find the minutes <a moz-do-not-send="true"
href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_June_2,_2020#Minutes">here</a>
and below.</p>
<p> -- Mark</p>
<p>
</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">HDGeant4 Meeting, June 2, 2020, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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lang="en">
<p>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
</p>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/9Vixr/">recording of
this meeting</a> on the BlueJeans site. Use your JLab
credentials to get access.
</p>
<h3><span class="mw-headline"
id="Review_of_minutes_from_the_last_Meeting">Review of
minutes from the last Meeting</span></h3>
<p>We went over <a
href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_May_19,_2020#Minutes"
title="HDGeant4 Meeting, May 19, 2020">the minutes
from May 19</a> without much discussion.
</p>
<h3><span class="mw-headline" id="Issues_on_GitHub">Issues
on GitHub</span></h3>
<p>We reviewed some of <a rel="nofollow" class="external
text"
href="https://github.com/JeffersonLab/HDGeant4/issues">the
issues</a>.
</p>
<ul>
<li> <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/152">Issue
#152</a>: 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.</li>
<li> <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/149">Issue
#149</a>: 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.</li>
<li> <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/143">Issue
#143</a>: 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<sup>0</sup>
particle gun. Richard will look into this one again.</li>
<li> <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/111">Issue
#111</a>: 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<sup>−</sup>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.</li>
<li> <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/93">Issue
#93</a>: 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.</li>
</ul>
<h3><span class="mw-headline"
id="Bethe-Heitler_Generator_in_HDGeant4">Bethe-Heitler
Generator in HDGeant4</span></h3>
<p>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
href="https://halldweb.jlab.org/wiki/index.php/HOWTO_generate_Bethe-Heitler_pairs_in_the_GlueX_target"
title="HOWTO generate Bethe-Heitler pairs in the GlueX
target">a HOWTO</a> on how to run the new generator.
</p>
<h3><span class="mw-headline" id="Event_Vertex_Simulation">Event
Vertex Simulation</span></h3>
<p>Alex initiated a discussion of <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/pull/156">Pull
Request #156</a>: 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 <a
rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/halld_recon/issues/381">halld_recon
Issue #381</a>. This has likely affected some of our
reconstructed data.
</p>
<p>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.
</p>
<h3><span class="mw-headline" id="Action_Item_Review">Action
Item Review</span></h3>
<ol>
<li> Ask Peter Pauli to close Issue #149 (Mark)</li>
<li> Study timing in the FCAL and BCAL as a function of
momentum. (Colin)</li>
<li> Create a custom branch of hdgeant4 that does
ignores energy from low-energy neutrons and alphas.
(Colin, Richard)</li>
<li> Close Issue #93 and reference Issue #111 as a
continuation of the work. (Mark, Alex)</li>
<li> Discuss a scheme for setting the event vertex
position in the x-y plane in simulation. (all)</li>
</ol>
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