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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,_August_11,_2020#Minutes">here</a>
and below.</p>
<p> -- Mark</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">HDGeant4 Meeting, August 11, 2020, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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lang="en">
<p>Present: Alex Austregesilo, Sean Dobbs, Mark Ito
(chair), Igal Jaegle, Naomi Jarvis, Richard Jones,
Mahmoud Kamel, Churamani Paudel, Simon Taylor, Nilanga
Wickramaarachchi, Beni Zihlmann
</p>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/ziPr0UPh_Ww/">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 the <a
href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_July_14,_2020#Minutes"
title="HDGeant4 Meeting, July 14, 2020">minutes from
July 14</a>, a month ago now. Richard has made the
judgment that the problem with particle propagation not
being able to find the normal to a surface, reported as
a warning, occurs rarely enough that it should not cause
a problem for us. This we can live with.
</p>
<h3><span class="mw-headline" id="Issues_on_GitHub">Issues
on GitHub</span></h3>
<p>We reviewed <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/169">hdgeant4
hanging at first event</a>. This problem was
introduced in the effort to get reproducible results
from all hdgeant4 output events based on the two input
random number seeds. The application of mutex locks
introduced to use certain ROOT functionality involving
the ROOT random number generator had a bug. This is
now fixed. Igal will close the issue.</li>
<li> <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/167">G4
exceptions for certain run numbers</a>. We will
follow up with Elton on this issue. I may be due to
trying to reconstruct TOF-II data with
TOF-I-only-compatible software.</li>
<li> <a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/111">Difference
in Acceptance between G3 and G4</a>. Colin Gleason's
last post on this issue showed a large difference in
overall event acceptance if simulated with Richard's
"no heavy light" branch. The acceptance goes down by a
factor of several. We will likely need further
guidance from Colin on what particles in the event are
creating the difference.</li>
</ul>
<h3><span class="mw-headline"
id="Holes_in_.CE.B3.CE.B3.E2.86.92.CE.B7_Invariant_Mass">Holes
in γγ→η Invariant Mass</span></h3>
<p>Mahmoud showed an anomaly in the two-photon invariant
mass distribution near the η. There are dips on either
side of the η mass. See his figure below (lower left
plot). The dips come from two regions of beam photon
energy which are near the corresponding boundaries
between the tagger microscope and hodoscope. The regions
show as dark blue in the lower right plot. There may
some issue with some kind of subtraction from the data
since the holes have negative entries in the histogram.
Mahmoud will enter this as an issue. </p>
<p><a
href="https://halldweb.jlab.org/wiki/index.php/File:Hdgeant_8_11_2020.png"
class="image"><img alt="Hdgeant 8 11 2020.png"
src="https://halldweb.jlab.org/wiki/images/thumb/e/e5/Hdgeant_8_11_2020.png/600px-Hdgeant_8_11_2020.png"
width="600" height="338"></a>
</p>
<p>Added in press: this is now <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/173">Issue
#173</a>.
</p>
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