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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,_April_9,_2019#Minutes">here</a>
and below.</p>
<p> -- Mark</p>
<p><><><><><><><><><><><><><><><><><><></p>
<p>
</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">HDGeant4 Meeting Minutes, April 9, 2019</span></h2>
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lang="en">
<p>Present:
</p>
<ul>
<li> <b>CMU: </b> Naomi Jarvis</li>
<li> <b> Glasgow: </b> Peter Pauli</li>
<li> <b> JLab: </b> Alex Austregesilo, Thomas Britton,
Mark Dalton, Stuart Fegan, Mark Ito (chair), Simon
Taylor, Beni Zihlmann</li>
</ul>
<p>There is <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/5Ft48/">a recording of
this meeting</a> on the <a rel="nofollow"
class="external text"
href="https://jlab.bluejeans.com/">BlueJeans site</a>.
Use your JLab credentials to access it.
</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,_March_26,_2019#Minutes"
title="HDGeant4 Meeting, March 26, 2019">the minutes
from the March 26th meeting</a> without significant
comment.
</p>
<h3><span class="mw-headline"
id="Do-over_on_comparison_studies">Do-over on
comparison studies</span></h3>
<p>Simon is working on analysis of his particle gun
simulations.
</p>
<h3><span class="mw-headline"
id="Geant3.2F4_comparisons_for_the_K-.2C_K.2B_and_p_particle_gun">Geant3/4
comparisons for the K-, K+ and p particle gun</span></h3>
<p>Peter led us though <a rel="nofollow" class="external
text"
href="https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=3964">the
set of summary slides</a> from his particle gun
studies. He chose protons and charged kaons because they
are relevant to his analysis. Further he chose kinematic
regions for each that match his reaction. He created
monitoring plots for each species and had posted the
complete set of plots for each as part of his GlueX
Note.
</p>
<p>The summary alone runs to 72 slides and we went through
them all in the course of about an hour. The secretary
does not have detailed notes on each slide, but will
record here some general remarks:
</p>
<ul>
<li> Peter told us he chose plots that seemed
interesting, either because they showed good agreement
between GEANT and Geant4 or, more likely, because
there were puzzling differences.</li>
<li> As a general guide, if two plots are shown on the
same pad, the blue is GEANT and the red is Geant4. If
there are two separate pads, then the top is GEANT,
the bottom is Geant4.</li>
<li> He sees a charged particle reconstruction
efficiency for Geant4 that is about 10% lower than
that for GEANT. Alex noted that this is similar to
what he is seeing when he studies ρ<sup>0</sup>
events.</li>
<li> Peter mentioned that the differences he picked out
are mostly of two broad classes: (1) energy or (2)
timing, in each case as measured by the calorimeters.</li>
<li> We noted that since the z-position of charged
particles is not well measured for single particles,
some the the timing distributions may be hard to
understand. Still they should have similar features in
GEANT vs. Geant4.</li>
<li> The versions of the code he used came before <a
rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/pull/100">Richard's
most recent pull request</a>, symmetrizing the
treatment of timing between the FCAL and BCAL. Some of
the differences may have lessened in the new code;
this should be checked.</li>
</ul>
<p>Please consult the recording if interested in a
plot-by-plot discussion.
</p>
<h3><span class="mw-headline"
id="Issue_on_GitHub:_missing_thrown_events">Issue on
GitHub: missing thrown events</span></h3>
<p>Thomas called our attention to <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/101">Issue
#101 on GitHub</a>, "Differences between G3 and G4 in
eta.pi," submitted by Carlos Salgado. Carlos sees a
completely different thrown momentum distribution for
protons when using GEANT vs. Geant4 even though the
generated events are identical in the two cases. Indeed
they come from the same HDDM file.
</p>
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