[Halld-tagger] [EXTERNAL] Re: About monitoring of the photon circular polarization

Wed Oct 14 08:58:13 EDT 2020

Hi all,

I agree that this is potentially promising and I am also impressed by how large the analyzing power is in this configuration.  However, this is something that would need to be studied in detail.

In the Compton polarimetry that we are used to in Halls A and C, the energy of both incoming particles is known.  The tricks that are employed are to either integrate over the outgoing photon energies or to measure the shape of the electron spectrum.  Very seldom are both outgoing particles detected together even for diagnostics.  I’m not aware of an asymmetry ever being done using both particles in coincidence, anywhere in the world.

In Hall D the energy of the incoming photon would be unknown.  We would need to detect both the outgoing particles and with enough resolution to reconstruct both the energy of the incoming photon and the kinematics of the outgoing particles so that the expected analyzing power would be known.  Note how quickly it varies with photon angle before the rate disappears.  The products are produced with such small angles that for PRIMEX most of the length of the hall is used to detect them.  We would need to find a way to detect the photons upstream of the target.

So, it’s not an insignificant challenge, although not having to produce a complicated laser setup and thread an electron beam through it would certainly be easier.

Best,
Mark

On Oct 14, 2020, at 7:19 AM, Richard Jones <richard.t.jones at uconn.edu<mailto:richard.t.jones at uconn.edu>> wrote:

Eugene and all,

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.

-Richard

On Wed, Oct 14, 2020 at 7:16 AM Richard Jones <rjones30 at gmail.com<mailto:rjones30 at gmail.com>> wrote:
Eugene and all,

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.

-Richard

On Wed, Oct 14, 2020 at 3:06 AM Eugene Chudakov <gen at jlab.org<mailto:gen at jlab.org>> wrote:

*Message sent from a system outside of UConn.*

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.

Eugene

_______________________________________________
Halld-tagger mailing list
Halld-tagger at jlab.org<mailto:Halld-tagger at jlab.org>
https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmailman.jlab.org%2Fmailman%2Flistinfo%2Fhalld-tagger&data=04%7C01%7Crichard.t.jones%40uconn.edu%7Ce0254b50fc0a48d2e7fd08d8700fa3d0%7C17f1a87e2a254eaab9df9d439034b080%7C0%7C0%7C637382559877244273%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=M3QGQPslYlaM7GemKET%2BQiO1kp4OWrS7GCKLdzGP%2F3w%3D&reserved=0<https://urldefense.proofpoint.com/v2/url?u=https-3A__nam10.safelinks.protection.outlook.com_-3Furl-3Dhttps-253A-252F-252Fmailman.jlab.org-252Fmailman-252Flistinfo-252Fhalld-2Dtagger-26amp-3Bdata-3D04-257C01-257Crichard.t.jones-2540uconn.edu-257Ce0254b50fc0a48d2e7fd08d8700fa3d0-257C17f1a87e2a254eaab9df9d439034b080-257C0-257C0-257C637382559877244273-257CUnknown-257CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0-253D-257C1000-26amp-3Bsdata-3DM3QGQPslYlaM7GemKET-252BQiO1kp4OWrS7GCKLdzGP-252F3w-253D-26amp-3Breserved-3D0&d=DwMFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=-MwMW0sKroUIjy-Lh9rb3KzmWIgdcbbr9_jez8RLmto&m=MvPeTLcG2bi2qeMw97Y0X0yroLwtiZ43x_9ojlGB7FY&s=ukcFhWv_GcqL-itGqtF1zHNgt3hzCiiEFm3T6qT7yAY&e=>
_______________________________________________
Halld-tagger mailing list
Halld-tagger at jlab.org<mailto:Halld-tagger at jlab.org>
https://mailman.jlab.org/mailman/listinfo/halld-tagger

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.jlab.org/pipermail/halld-tagger/attachments/20201014/4f86c7b7/attachment-0001.html>