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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,_December_1,_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, December 1, 2020, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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<div id="mw-content-text" dir="ltr" class="mw-content-ltr"
lang="en">
<p>Present: Alex Austregesilo, Tegan Beattie, Sean Dobbs,
Colin Gleason, Mark Ito (chair), Igal Jaegle, Naomi
Jarvis, Richard Jones, Zisis Papandreou, Simon Taylor,
Beni Zihlmann
</p>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/mQ@IoAghvqn/">recording
of this meeting</a> on the BlueJeans site. Use your
JLab credentials to get access.
</p>
<h3><span class="mw-headline" id="Announcements">Announcements</span></h3>
<p>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.
</p>
<ul>
<li> The directories are in the standard place on the
group disk:</li>
</ul>
<pre>/group/halld/Software/builds/Linux_CentOS8-x86_64-gcc8.3.1-cntr
</pre>
<ul>
<li> The build is now getting shipped to Oasis and is
available via CVMFS.</li>
<li> The corresponding singularity container is in the
"dist" directory:</li>
</ul>
<pre>/group/halld/www/halldweb/html/dist/gluex_centos-8.2.2004_sng3.6_gin2.15.sif
</pre>
<p>and is available for download from
</p>
<pre> <a rel="nofollow" class="external free" href="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</a>
</pre>
<p>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.
</p>
<ul>
<li> 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.</li>
<li> 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.</li>
<li> 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.</li>
<li> 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.</li>
<li> 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.</li>
<li> Sean advocated an approach where we specify a
minimum compiler version as a starting point and work
on guidance for every to get there. </li>
<li> Mark will continue to think about a recommendation
for best practices. He found the discussion very
useful in this regard.</li>
</ul>
<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,_September_22,_2020#Minutes"
title="HDGeant4 Meeting, September 22, 2020">the
minutes from September 22</a>. Sean mentioned that the
details on how to widen the Δt cuts to make efficiency
calculations more reliable was taken up at <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_PID_Meeting,_December_1,_2020"
title="GlueX PID Meeting, December 1, 2020">the PID
meeting this morning</a>.
</p>
<h3><span class="mw-headline" id="Issues_on_GitHub">Issues
on GitHub</span></h3>
<p>We spent most of the remaining time discussing <a
rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/111">Issue
#111</a>, <b>Difference in Acceptance between G3 and
G4</b> 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.]
</p>
<p>There followed an active discussion of ideas related to
the issue.
</p>
<ul>
<li> 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.</li>
<li> 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.</li>
<li> 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.</li>
<li> Colin had two suggestions for further studies.
<ol>
<li> Rather than looking as the relatively
complicated topology of γp→ηπ<sup>−</sup>Δ<sup>++</sup>,
we drop back to a single particle gun study
inspired by differences seen in the full reaction.</li>
<li> On and event-by-event basis, study where the
cuts differ when using different hadronic
interaction models for the same event.</li>
</ol>
</li>
<li> Richard also had suggestions on what to try next:
<ol>
<li> 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.</li>
<li> 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.</li>
</ol>
</li>
<li> Sean reminded us of <a rel="nofollow"
class="external text"
href="https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=4053">a
talk that Mark Dalton gave at a GlueX workshop</a>
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.</li>
<li> 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.</li>
<li> The group thanked Zisis for getting the group fired
up to re-address these issues and also welcomed Tegan
to the effort.</li>
</ul>
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