[Frost] Photon polarization issue?

[Ken Livingston]

Hi Michael,
I've just had a look at this. As you probably know, the polarisation for 
this beamtime, in general, was much lower than expected. Mark Anderson 
and I spent a long time agonising over this. I initially suspected that 
the data we were using for the fits was contaminated by randoms (in 
uncollimated), resulting in a measured polarization that was lower that 
the actual beam polarization. We tried several methods to check that 
this was not the case, and in the end, in Priya's analysis, the measured 
polarizations gave reasonable comparison with g8, where there was 
overlap (as you point out).

The fit's don't look any worse for the lower energy points - in fact 
they look pretty reasonable 
(https://urldefense.proofpoint.com/v2/url?u=http-3A__nuclear.gla.ac.uk_-7Emarka_g9b-5Fpol-5Fplots_beamPolPass1.html&d=DwICaQ&c=lz9TcOasaINaaC3U7FbMev2lsutwpI4--09aP8Lu18s&r=zQqa9I5mt1K7-QfsuuBIXw&m=NaGgX1hr870oOOeNi6LYFvzPDILKL7ibK3O9y6ycARQ&s=r_NdgH9gQS5pXKUsn_0BWWtfjhZRIyHE0DS2UwVBga8&e= )
But, from your comparison with previous photon asymmetry measurements, 
the polarization is clearly "undermeasured" for the 900 and 1100 settings.

I agree that the best solution is to renormalise as you suggest in slide 
10 of your presentation.

Regards,
Ken


On 28/12/17 18:29, Michael Dugger wrote:
>
> Hi,
>
> I hope that the Holiday season is going well for everyone.
>
> We have been looking at the g9b data and think there is a problem with 
> the polarization for the linear photon beam using the 900 and 1100 MeV 
> coherent edge settings.
>
> Since the discussion of the potential polarization issue requires 
> graphics, I have put together a pdf describing the situation. The pdf 
> can be found at
>
> https://userweb.jlab.org/~dugger/frost/pipSigma.pdf
>
> Comments and suggestions are welcomed.
>
> Thanks for your time.
>
> Sincerely,
> Michael
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-- 
=======================================================
Ken Livingston

Dept. of Physics & Astronomy,        Tel: +44 141 330 6428
University of Glasgow,               Fax: +44 141 330 5889
Glasgow G12 8QQ.
Scotland. UK.
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