<div dir="ltr">Eugene and all,<div><br></div><div>Yes, that could work, I was not aware the Compton analyzing power is so high for 3 GeV photons. I think what they have in Hall A is different. The Hall A Compton is using a circularly polarized laser beam amplified in a cavity to measure the electron beam circular polarization. In the Hall A Compton, the analyzing power for electron beam circular polarization is a few percent, much lower than what Eugene showed for a 3 GeV photon beam. So measuring directly the photon beam circular polarization is potentially much easier than what they do in Hall A/C. We would probably do it using a setup similar to what Primex has for their Compton measurement, and we would just need to be able to insert a polarized foil into the beam. Interesting, sounds relatively simple and cheap.</div><div><br></div><div>-Richard</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Oct 14, 2020 at 7:16 AM Richard Jones <<a href="mailto:rjones30@gmail.com">rjones30@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Eugene and all,<div><br></div><div>Yes, that could work, I was not aware the Compton analyzing power is so high for 3 GeV photons. I think what they have in Hall A is different. The Hall A Compton is using a circularly polarized laser beam amplified in a cavity to measure the electron beam circular polarization. In the Hall A Compton, the analyzing power for electron beam circular polarization is a few percent, much lower than what Eugene showed for a 3 GeV photon beam. So measuring directly the photon beam circular polarization is potentially much easier than what they do in Hall A/C. We would probably do it using a setup similar to what Primex has for their Compton measurement, and we would just need to be able to insert a polarized foil into the beam. Interesting, sounds relatively simple and cheap.</div><div><br></div><div>-Richard</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Oct 14, 2020 at 3:06 AM Eugene Chudakov <<a href="mailto:gen@jlab.org" target="_blank">gen@jlab.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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I mentioned at the beam meeting that one can potentially detect/monitore the circular polarization of a photon beam, but did not remember the details. Meanwhile, I recalled it - one can use the Compton scattering on longitudinally polarized electrons (in iron).
I attach a few plots showing the kinematics, the cross section and the analyzing power. I do not know at this time whether it is practical or not for the GDH project.</div>
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Eugene</div>
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