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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_29,_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, June 29, 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), Richard Jones, Zisis Papandreou, Simon

                Taylor, Jon Zarling, Beni Zihlmann

              </p>

              <p>There is a <a rel="nofollow" class="external text" href="https://bluejeans.com/s/Rho3x4PNH1b/">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,_June_15,_2021#Minutes" title="HDGeant4 Meeting, June 15, 2021">minutes from

                  the meeting on June 15</a>.

              </p>

              <p>We discussed what combination of versions we should aim

                at for the next major upgrade. We settled on the

                following:

              </p>

              <ul>

                <li> GCC 8.x</li>

                <li> ROOT 6.24.x</li>

                <li> Geant4 10.06.x</li>

              </ul>

              <p>The recommended Linux distribution is CentOS 7 with <a rel="nofollow" class="external text" href="https://www.softwarecollections.org/en/scls/rhscl/devtoolset-8/">Developer

                  Toolset 8</a> (to provide GCC 8). A Singularity

                container with this combination has been built.

              </p>

              <h3><span class="mw-headline" id="Charged_hadron_timing_in_the_BCAL">Charged hadron

                  timing in the BCAL</span></h3>

              <p>Tegan showed his start at looking at charged hadrons in

                the reaction γp→π<sup>−</sup>Δ<sup>++</sup>. He has been

                working with Jon to set up the apparatus up to compare

                simulation with real data. He showed some preliminary

                plots that show good agreement. Notably he sees some

                double peaks in timing for data, probably due to

                proton/pion mis-identification, and those same peaks

                seem to be there in the simulation as well. See his

                plots in the recording.

              </p>

              <p>Tegan observed that with the good agreement he is

                seeing between simulation and data in single particle

                studies it becomes even more interesting to revisit the

                original studies of event efficiency that started us on

                this path.

              </p>

              <h3><span class="mw-headline" id="Comparison_of_Models_of_Polarized_Bethe-Heitler_Production">Comparison

                  of Models of Polarized Bethe-Heitler Production</span></h3>

              <p>Richard showed recent work comparing simulated

                Bethe-Heitler events between his Diracxx package and a

                generator built into a recent version of Geant4. He has

                reason to believe that the "Butler" model in G4 is close

                to that used by Andrew Schick in his simulations, which

                Andrew got from Rory Miskimen. The Butler model ignores

                the nuclear form factor, whereas it is taken into

                account in the Diracxx-based program. Richard sees the

                expected suppression of the cross section due to the

                form factor at high pair mass, where GlueX has

                acceptance, by a factor of a few compared to Butler. He

                sees agreement in the analyzing power predicted by the

                two models. He plans on giving a more comprehensive

                description of this work at the next Beamline Working

                Group meeting.

              </p>

              <h3><span class="mw-headline" id="Action_Items">Action

                  Items</span></h3>

              <ol>

                <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 further about how to get to modern versions

                  of external software packages. (all)</li>

              </ol>

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