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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,_May_4,_2021#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, May 4, 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, Lubomir Pentchev, Simon Taylor, Nilanga
Wickramaarachchi, Beni Zihlmann
</p>
<p>There is a <a rel="nofollow" class="external text" href="https://bluejeans.com/s/smXkAPjiI7L/">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,_April_6,_2021#Minutes" title="HDGeant4 Meeting, April 6, 2021">minutes from
the meeting on April 6</a>. Tegan will continue his
studies using the software for analysis launch version
38 with its wider timing window, dropping back from
version 40. He will get it running on the JLab farm.
</p>
<h3><span class="mw-headline" id="Simulating_Hit_Efficiency_for_the_FDC">Simulating
Hit Efficiency for the FDC</span></h3>
<p>Lubomir presented <a rel="nofollow" class="external
text" href="https://www.jlab.org/Hall-D/detector/fdc/FDC_tracking_Apr22.pdf">Garfield
studies</a> from which he derives hit efficiency as a
function of distance from the wire. This work was
previously presented at the Tracking Meeting.
</p>
<p>He showed an example track passing through a cell (page
2) which demonstrates the variation in drift
trajectories. He showed the efficiency as a function of
DOCA for various track angles (page 3). Here there is
not much variation in the behavior as a function of
angle. The main source of inefficiency is that for large
drift distances, ionization arrives at the wire over an
extended time, due to diffusion (page 4). That in turn
leads to a lower peak pulse height even though the
integrated charge collected may not be much different
from ionization that travels a shorter distance. The
lower peak pulse height may not cross the hit threshold,
causing the hit to be lost. One consequence is that the
efficiency has a strong dependence on the applied
threshold.
</p>
<p>At present, in the simulation this effect is not there.
Any reduction in efficiency will come only from tracks
having a small path inside a cell. In simulation, this
explains the much sharper drop in efficiency as a
function of DOCA compared to that seen in Lubomir's
result.
</p>
<p>Richard pointed out that there is an energy threshold
of sorts applied in HDGeant4 on energy loss in a cell
summed over all particles that traverse the cell
(multiple tracks from the event, or accidentals), but
this does not take into account the reduced probability
of threshold crossing due to large diffusion for long
drift distances.
</p>
<p>Lubomir's plots show the coefficients of his
parametrization of efficiency. Richard will take a stab
at incorporating the efficiency curves into mcsmear.
</p>
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