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Hi Asar,</div>
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We were talked yesterday about the difficulty of alignment, finding tracks and measuring efficiency with only 3 GEMs. It seemed like you were saying it was nearly impossible and we discussed the possibility of installing the 4<sup>th</sup> GEM plane as well
to allow for redundancy for track finding. One thing we didn't discuss is the Moller trigger. I'm not sure if the Moller coincidence trigger would obviate the necessity of a 4<sup>th</sup> plane. We have a very clean left-right coincidence trigger for the
Moller electron pairs. The accidental rate is typically <1%. The electrons contributing to the trigger in MOLLER will cover an area of only a few square cm (<20cm^2 per side) of the GEMs due to a limiting collimator we will install. I don't have a good feeling
for how many X-rays or low energy single-arm electrons will hit the GEMs, but if we have a 2-4kHz source of electron Moller pairs as our GEM trigger and a phase space of only a few square cm, I am wondering what you think about finding tracks then with only
3 planes. One complicating factor is that there might be a gentle curvature of tracks due to fringe field of the dipole spectrometer magnet.</div>
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-Don</div>
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Donald Jones</div>
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Hall A/C Staff Scientist</div>
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Jefferson Lab</div>
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Newport News, VA</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Asar Ahmed <asar@jlab.org><br>
<b>Sent:</b> Monday, May 4, 2026 1:46 PM<br>
<b>To:</b> Donald Jones <jonesdc@jlab.org><br>
<b>Cc:</b> halla_molpol@jlab.org <halla_molpol@jlab.org>; thejimnap@gmail.com <thejimnap@gmail.com><br>
<b>Subject:</b> Re: Hall A Moller polarimetry meeting at 1PM</font>
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<div style="line-break:after-white-space">Hi Don
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<div>Please find the slides.</div>
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<div>Best regards</div>
<div>Asar<br id="x_x_lineBreakAtBeginningOfMessage">
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<div>On May 4, 2026, at 8:28 AM, Donald Jones <jonesdc@jlab.org> wrote:</div>
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Hi Folks,</div>
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We will have our usual Hall A Moller polarimetry meeting today at 1PM.</div>
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<a href="https://jlab-org.zoomgov.com/j/1606426957">https://jlab-org.zoomgov.com/j/1606426957</a></div>
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Passcode: 314159</div>
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-Don</div>
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Donald Jones</div>
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Hall A/C Staff Scientist</div>
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Jefferson Lab</div>
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Newport News, VA</div>
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