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<p>Folks,</p>
<p>Please find the minutes from last week's HDGeant4 Meeting <a
moz-do-not-send="true"
href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_May_19,_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, May 19, 2020,</span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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<p>Present: Alex Austregesilo, Sean Dobbs, Colin Gleason,
Mark Ito (chair), Naomi Jarvis, Richard Jones, Churamani
Paudel, Joerg Reinhold, Justin Stevens, Simon Taylor,
Nilanga Wickramaarachchi, Beni Zihlmann
</p>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/TByqC/">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 [[HDGeant4 Meeting, May 5,
2020#Minutes|the minutes from May 5].
</p>
<ul>
<li> Nilanga will close <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/137">Issue
#137</a>, "K particle gun request to resolve G3/G4
difference near p 0.5 GeV/c and theta 120 degrees" and
re-open it as a halld_recon issue. There is concern
about loss of tracking efficiency in the backward
region of the CDC.</li>
</ul>
<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>
<h4><span class="mw-headline"
id="Difference_in_Acceptance_between_G3_and_G4_.23111">Difference
in Acceptance between G3 and G4 #111</span></h4>
<p>We noted the one-year anniversary of <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/111">this
issue</a>. We started with comments entered yesterday
(Monday). Colin showed plots where the acceptance of
charged pions can vary as much between the two hadronic
codes in Geant3 as from that in Geant4. Protons look
similar among the three.
</p>
<p>Richard commented that response of the calorimeters
could depend on the details of very low energy
processes, including those of alphas and neutrons and
for the BCAL, that response depend a lot on whether the
interactions take place in the lead or in the
scintillator. Recall that the simulated BCAL is composed
of a fictional, average lead-scintillator compound.
Saturation in the scintillator may be in play as well.
For the Cerenkov response of the FCAL there are similar
uncertainties for the response to low energy processes.
</p>
<p>Sean suggested removing the requirement of matching of
charged particles to one of the outer detectors as a
cross-check on the acceptance.
</p>
<p>Colin also showed timing distribution of the various
particle species in his reaction. Differences in the
photon timing resolution function for the BCAL are seen
between data and all Monte Carlo samples, a difference
that was not expected and needs to be explored further.
He also showed comparisons for timing from the
time-of-flight. Here the pi<sup>−</sup> show a wide
distribution for data than for Monte Carlo.
</p>
<h3><span class="mw-headline" id="BCAL_Timing">BCAL Timing</span></h3>
<p>Sean showed <a rel="nofollow" class="external text"
href="https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=4053">some
slides from Mark Dalton</a>, shown at the May 16, 2019
Collaboration Meeting (one year ago), showing
comparisons between data and simulations of timing
resolution for both neutral showers and charged
particles. He also showed offsets as a function of
energy, z, and run number for both neutral showers and
charged showers. He presented them as outstanding
puzzles that this group might want to address.
</p>
<h3><span class="mw-headline" id="Pull_Requests_on_GitHub">Pull
Requests on GitHub</span></h3>
<p>We looked at <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/pulls">pull
requests</a>. Richard has <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/pull/153">introduced
a new card</a> to allow users to use the CCDB to
specify the vertex position in the transverse plane as
well as the x and y spread of the beam. The information
comes from the measured position of two track vertices
found in the tracking, a facility developed by Simon.
</p>
<p>Justin pointed out that this feature should be
accessible via MCwrapper.
</p>
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