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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_1,_2021#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, June 1, 2021, </span><span class="mw-headline" id="Minutes">Minutes</span></h2>
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<p>Present: Alex Austregesilo, Tegan Beattie, Sean Dobbs,
Mark Ito (chair), Igal Jaegle, Richard Jones, Zisis
Papandreou, Simon Taylor, Beni Zihlmann
</p>
<p>There is a <a rel="nofollow" class="external text" href="https://bluejeans.com/s/IlW47yET1A6/">recording
of this meeting</a> on the BlueJeans site. Log into
the <a rel="nofollow" class="external text" href="https://jlab.bluejeans.com">BlueJeans site</a>
first to gain access (use your JLab credentials).
</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 the <a href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_May_18,_2021#Minutes" title="HDGeant4 Meeting, May 18, 2021">minutes from
the meeting on May 18</a> without a lot of discussion.
</p>
<h3><span class="mw-headline" id="Charged_Hadrons_and_BCAL_Timing">Charged Hadrons
and BCAL Timing</span></h3>
<p>Tegan showed several plots, which he previewed at the
last meeting, comparing timing distributions for charged
hadrons between data and Monte Carlo. On the simulation
side he plots both Geant4 and GEANT/HADR4. He used
exclusive ρ events for both data and MC. He plots the
difference in the time predicted by charged particle
tracking to that measured in the BCAL.
</p>
<ul>
<li> For protons the agreement in the core Gaussian part
of the distributions is good for all three species;
see <a href="https://halldweb.jlab.org/wiki/images/4/46/Proton_tegan.pdf" class="internal" title="Proton tegan.pdf">this plot</a>.
The data does show non-Gaussian tails on the log plot
shown that could be due to event selection. We
suggested that he try a tighter cut on the χ<sup>2</sup>
of the kinematic fit to see if that reduces the tails.
Tegan reported that on a linear plot, these tails are
not visible to the eye.</li>
<li> For pions the agreement among all three is very
good, with a high side tail visible in all three
species; see <a href="https://halldweb.jlab.org/wiki/images/a/a6/PiPlus_tegan.pdf" class="internal" title="PiPlus tegan.pdf">this plot</a>.</li>
</ul>
<p>Mark suggested that if Tegan does not uncover further
problems, we should go back to the original studies of
event efficiency that launched us on this path. Those
studies showed overall event reconstruction efficiency
showing large differences between the various simulation
engines. We have since concluded that GEANT/HADR1 does
not give reliable timing distributions for charged
hadrons in the calorimeters, but the comparison between
Geant4 and GEANT/HADR4 is still relevant. There have
been many changes in the code since those studies were
performed and we should see where we stand with the
latest versions. Zisis mentioned that Ahmed Foda's ωπ
analysis shows good agreement in cross sections between
Spring 17, Spring 18, and Fall 18 lately, a new
development.
</p>
<h3><span class="mw-headline" id="The_Schick_Effect">The
Schick Effect</span></h3>
<p>We discuss the problem Andrew Schick discovered in his
Bethe-Heitler analysis where the total energy of the B-H
pairs in the FCAL were lower than the beam photon beam
energy by 4 to 5%. Even in simulation some of this
deficit is seen, though only by 1 to 2%. Beni mentioned
that there is also a difference seen between electrons
and positrons. Alex also reminded us that Drew Smith
(Compton scattering) and Mark Dalton (ω production) both
showed effects in the cross sections that pointed to
inefficiencies in the inner blocks of the FCAL.
</p>
<p>At this meeting, the question was whether there might
be some insight to be gained by studying these effects
in simulation in the future.
</p>
<h3><span class="mw-headline" id="Simulation_GlueX_Doc">Simulation
GlueX Doc</span></h3>
<p>Richard floated the idea of the group writing a GlueX
Doc summarizing the knowledge gain by this group
vis-a-vis the fidelity of our simulation so that the
ideas don't get lost. This would be along the lines of
the document being produced by the Beamline Working
Group on beamline-related systematics.
</p>
<h3><span class="mw-headline" id="Exploiting_New_Features_of_Geant4">Exploiting New
Features of Geant4</span></h3>
<p>Richard reported on work he has been doing to
incorporate circular polarization into the simulation.
One aspect of his work is to use recently introduced
polarization dependent cross sections from Geant4. He
finds that it is sufficient to go to version 10.6.p1 to
pick these up, but that requires GCC 5.3.1 (again
sufficient if not necessary) which is beyond that
provided by CentOS 7. He is using Devtoolset 4[?] to get
the compiler. He stressed the need for GlueX to press
forward with using more modern versions of Geant4 and
other packages.
</p>
<h3><span class="mw-headline" id="Bethe-Heitler_Event_Generator">Bethe-Heitler Event
Generator</span></h3>
<p>Richard has been working on a built-in Bethe-Heitler
generator for HDGeant4. This is to support Andrew's
work, mentioned above, with a more accurate physics
model that the one Andrew has been using thus far.
</p>
<h3><span class="mw-headline" id="Action_Items">Action
Items</span></h3>
<ol>
<li> Re-do proton-in-BCAL timing study with tighter cuts
on the χ<sup>2</sup> from the kinematic fit. (Tegan)</li>
<li> Re-do comparisons of overall event reconstruction
efficiencies.</li>
<li> Think about how to study the Schick-Smith-Dalton
effect(s). (all)</li>
<li> Think about a GlueX Doc on simulation. (all)</li>
<li> Think about how to get to modern versions of
external software packages. (all)</li>
</ol>
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