<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<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_10,_2021#Minutes">here</a>
and below.</p>
<p> -- Mark</p>
<p> ___________________________________</p>
<p>
</p>
<div id="globalWrapper">
<div id="column-content">
<div id="content" class="mw-body" role="main">
<h2 id="firstHeading" class="firstHeading" lang="en"><span dir="auto">HDGeant4 Meeting, August 10, 2021, </span><span class="mw-headline" id="Minutes">Minutes</span></h2>
<div id="bodyContent" class="mw-body-content">
<div id="mw-content-text" dir="ltr" class="mw-content-ltr" lang="en">
<p>Present: Alex Austregesilo, Tegan Beattie, Mark Ito
(chair), Igal Jaegle, Richard Jones, Simon Taylor, Beni
Zihlmann
</p>
<p>There is a <a rel="nofollow" class="external text" href="https://bluejeans.com/s/g3GZp4pSoHn/">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 reviewed the <a href="https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_July_13,_2021#Minutes" title="HDGeant4 Meeting, July 13, 2021">minutes from
the meeting on July 13</a>.
</p>
<p>Mark has succeeded building the GlueX software stack
with ROOT 6.24.0 and Geant4 10.06.p01 using GCC 8 using
three different methods:
</p>
<ol>
<li> On a CentOS 7 singularity container with Developers
Toolset 8. This was <a rel="nofollow" class="external
text" href="https://mailman.jlab.org/pipermail/halld-offline/2021-July/008587.html">announced
on the offline list</a>.</li>
<li> Using GCC 8.3.0 supplied by a module on the ifarm.</li>
<li> Using a CentOS 8 singularity container using its
native GCC, 8.3.1</li>
</ol>
<p>We marked several issues as ready-to-be-closed. We need
to make sure that this is done.
</p>
<h3><span class="mw-headline" id="Efficiency_Tables">Efficiency
Tables</span></h3>
<p>Igal asked if there is a way to check if the correct
efficiency tables are being applied to simulated data.
He received guidance from Richard (use the MC variation
of the CCDB) and Alex (there are dead wire maps for the
FDC).
</p>
<h3><span class="mw-headline" id="Issue_.23181:_G3.2FG4_Difference_in_FDC_wire_efficiency_at_the_cell_boundary">Issue
#181: G3/G4 Difference in FDC wire efficiency at the
cell boundary</span></h3>
<p>There has been a lot of work on <a rel="nofollow" class="external text" href="https://github.com/JeffersonLab/HDGeant4/issues/181">this
issue</a>. It has morphed from a G3 vs. G4 comparison
question to an effort to do a faithful simulation of hit
efficiency as a function of track position in the cell.
</p>
<p>The process of changing the absolute level of the
efficiency curve to get agreement with data has
converged. It was complicated by the fact that changing
the level affected both the numerator and denominator in
the "efficiency" measure used in the comparison. This is
probably due to the measure requiring 4 of 6 hits in any
package being considered; a loss of a single hit could
significantly reduce the number of "tracks" being
considered.
</p>
<p>Richard also repeated the comparison between data and
Monte Carlo with a recent version of tracking using
bggen MC to compare with the ρ data used in all other
studies. Here the "efficiency" measure was higher that
that obtained by Alex with a much older version of
reconstruction, but the agreement between data and MC
was just as good.
</p>
<p>Alex will do a check that he gets a similar result with
bggen simulated, including random triggers in the
simulation, a feature not present in Richard's study.
</p>
<p>In all we appear to be very close to closing this
issue.
</p>
<h3><span class="mw-headline" id="Issue_.23192:_Vertex_generation_used_with_BHgen">Issue
#192: Vertex generation used with BHgen</span></h3>
<p>Richard described work getting realistic generation of
Bethe-Heitler pairs (both electrons and muons) from a
lead target, as will be used for CPP, in response to <a rel="nofollow" class="external text" href="https://github.com/JeffersonLab/HDGeant4/issues/192">this
issue</a>. The details of his effort are recorded in
his notes, in the section <a rel="nofollow" class="external text" href="https://docs.google.com/document/d/1BZXqLqZOFrPXhOB1g9E7H35y6A-nyRhufrskiCuVga0/edit#heading=h.dvtw9phxtnnb">New
pair converter targets</a>. He showed a model that
incorporates a nuclear form factor for elastic
scattering and for inelastic processes quasi-elastic
scattering from protons and neutrons, where the Fermi
motion of the nucleons is taken into account. He had
compared his model with one that comes from Geant4. The
Geant4 model does not have a nuclear form factor and has
no model for inelastic scattering. Richard sees
differences in the cross section as a function of Q<sup>2</sup>
which he attributes to these lacks in the Geant4 model.
</p>
<p>As a consistency check, he re-did the comparison,
restricting Q<sup>2</sup> to values less than 10<sup>-4</sup> (GeV/c)<sup>2</sup>.
In the this region the agreement between his model and
Geant4 is all but exact.
</p>
<h3><span class="mw-headline" id="Future_Projects">Future
Projects</span></h3>
<p>We (aka Richard (mainly)) discussed ideas for other
developments in simulation for GlueX.
</p>
<ul>
<li> General QED process event generator a la the BH
generator. User would be able to specify the process.
Like the BH generator, it would take into account the
spatial distribution of the photon energy and
polarization as a function of position of emergence
from the collimator.</li>
<li> Radiative corrections for cross section
measurements.</li>
<li> Neutrons and K<sub>L</sub>s.</li>
<li> CDC efficiency.</li>
<li> Variance and co-variance agreement between data and
simulation.</li>
</ul>
</div>
<br>
</div>
</div>
</div>
</div>
</body>
</html>