[Halla_molpol] Hall A Moller polarimetry meeting at 1PM

[Donald Jones]

Hi Asar,
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 4th 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 4th 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.
-Don

Donald Jones
Hall A/C Staff Scientist
Jefferson Lab
Newport News, VA
________________________________
From: Asar Ahmed <asar at jlab.org>
Sent: Monday, May 4, 2026 1:46 PM
To: Donald Jones <jonesdc at jlab.org>
Cc: halla_molpol at jlab.org <halla_molpol at jlab.org>; thejimnap at gmail.com <thejimnap at gmail.com>
Subject: Re: Hall A Moller polarimetry meeting at 1PM

Hi Don

Please find the slides.

Best regards
Asar

On May 4, 2026, at 8:28 AM, Donald Jones <jonesdc at jlab.org> wrote:

Hi Folks,
We will have our usual Hall A Moller polarimetry meeting today at 1PM.
https://jlab-org.zoomgov.com/j/1606426957
Passcode: 314159
-Don

Donald Jones
Hall A/C Staff Scientist
Jefferson Lab
Newport News, VA

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