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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,_January_15,_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, January 15, 2019, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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<p>Present:
</p>
<ul>
<li> <b> CMU: </b> Naomi Jarvis</li>
<li> <b> JLab: </b> Thomas Britton, Sean Dobbs, Mark
Ito (chair), Simon Taylor, Beni Zihlmann</li>
<li> <b> UConn: </b> Richard Jones</li>
</ul>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/zUbep/">recording of
this meeting</a> on the BlueJeans site. Use your JLab
credentials.
</p>
<h3><span class="mw-headline"
id="Review_of_minutes_from_last_time">Review of
minutes from last time</span></h3>
<p>We went over <a
href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_December_18,_2018#Minutes"
title="HDGeant4 Meeting, December 18, 2018">the
minutes from December 18</a> without significant
comment.
</p>
<h3><span class="mw-headline"
id="Nightly_cannot_run_MC_with_old_run_numbers_.28either_geant_3_or_geant_4.29">Nightly
cannot run MC with old run numbers (either geant 3 or
geant 4)</span></h3>
<p>Thomas reported that the simulation chain breaks
presently (current master branch) at the reconstruction
stage (i. e., hd_root). This turns out to be due to a
hard check on the presence of the DIRC geometry in
halld_recon; lack of the DIRC triggers an exit. This
needs to be relaxed. Sean volunteered to make the
change.
</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>
<h4><span class="mw-headline"
id="More_FDC_issues.3F_.2366">More FDC issues? #66</span></h4>
<p>Richard had several comments on <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/66">this
issue</a>.
</p>
<ul>
<li> Richard observed a problem, <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_Offline_Meeting,_September_18,_2018#Review_of_the_HDGeant4_Meeting_from_September_11"
title="GlueX Offline Meeting, September 18, 2018">first
reported by Beni</a>, where <b>pristine tracks,
headed into the meat of the FDC, leave no hits at
all</b>. Richard traced it to a Geant4 (G4) bug. Our
representation of the FDC has a internal volume in the
form of a cone to allow for cables whose volume
increases going upstream. The cone has a very small
apex angle. This triggers a condition in the G4 code
that finds intersections of lines with cones, one that
causes an exit if the discriminant of the quadratic
formula used in the calculation is too small (less
than 10<sup>−6</sup>. We are left with no hits at all.
The problem has been reported to the G4 Collaboration.
It has been corrected in our local of the G4 code.</li>
<li> The <b>indexing bug in the FDC</b> was <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_Software_Meeting,_January_8,_2019#Report_from_the_December_18_HDGeant4_Meeting"
title="GlueX Software Meeting, January 8, 2019">discussed
at the last Software Meeting</a>.</li>
<li> In the course of his HDGeant4 study, Richard
documented an anomaly in the track finding, again, <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_Offline_Meeting,_September_18,_2018#Review_of_the_HDGeant4_Meeting_from_September_11"
title="GlueX Offline Meeting, September 18, 2018">first
reported by Beni (same meeting as above)</a> where <b>many
hits in the FDC are not assigned to the track at the
wire-based stage of tracking,</b> but are recovered
at the time-based stage. These are all 4 GeV/c tracks
going at 5 degrees polar angle. For hdgeant, he sees
10% of the tracks have only less than 10 pseudo hits
associated with the track during the wire-based fit
out of the 24 possible hits. For hdgeant4, the
fraction is about 25%. In both cases the recovery in
the time-based fit is observed. This problem has not
been resolved, but neither is it a glaring difference
between the behavior of hdgeant and hdgeant4, nor does
it appear to affect track reconstruction efficiency
because of hit recovery at the time-based stage.</li>
<li> Richard also mentioned that when he goes to Geant4
version 10.04, he sees a significant increase in the
start-up time of hdgeant4, from 20 seconds to 2
minutes. He traced it back to a more aggressive
attempt to optimize the internal representation of the
geometry to speed up event generation. It is not clear
that we see much of this speed up. Richard introduced
a new card for control.in, GEOMOPT, that, when set to
0, will bypass optimization and make start-up faster.
This is useful when developing code. </li>
<li> Richard also reported that the upgrade to 10.04
requires changes to the use of the G4THitsMap class
due a change in the class interface. A large fraction
of our source code files had to get the the change, as
well as instrumentation to allow operation with older
versions of Geant4. Yuck.</li>
</ul>
<h4><span class="mw-headline"
id="Photon_energy_scale_.2367">Photon energy scale #67</span></h4>
<p>Richard has done <a rel="nofollow" class="external
text"
href="https://docs.google.com/presentation/d/1Ap0ifkk7GVCLq-EJuyXuSmxgsB2u-RNZmTU4et_WlFo/edit#slide=id.p">studies</a>,
presented at <a
href="https://halldweb.jlab.org/wiki/index.php/Jan_10,_2019_Calorimeter#Minutes"
title="Jan 10, 2019 Calorimeter">the last Calorimeter
Meeting</a> that address <a rel="nofollow"
class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/67">this
issue</a>. He sees no significant difference between
the single-shower response of hdgeant vs. that of
hdgeant4. He observed some systematic shifts as a
function of polar angle, but those are common to both
programs.
</p>
<p>Sean will revisit his original study and close the
issue if appropriate.
</p>
<h4><span class="mw-headline"
id="many_overlaps_in_the_GlueX_geometry_.2360">many
overlaps in the GlueX geometry #60</span></h4>
<p><a rel="nofollow" class="external text"
href="https://github.com/JeffersonLab/HDGeant4/issues/60">This
issue</a> was discussed at <a
href="https://halldweb.jlab.org/wiki/index.php/GlueX_Software_Meeting,_January_8,_2019#Announcements"
title="GlueX Software Meeting, January 8, 2019">the
last Software Meeting</a>. Richard has eliminated
overlaps and will close the issue.
</p>
<h3><span class="mw-headline" id="Switching_to_HDGeant4">Switching
to HDGeant4</span></h3>
<p>We seem to be close to being able to recommend HDGeant4
for regular use. For the DIRC data, there will be no
choice, of course. Sean recommended going back to our
original list of simulations to compare between HDG3 and
HDG4 and repeating them with the current code base. Mark
suggested that if the studies show agreement, we
document those results in a GlueX Doc which can be used
to back-up a recommendation for collaboration-wide use
of HDGeant4 by default. Thomas will look into firing up
his simulation runs again.
</p>
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