[Frost] Photon polarization issue?

[Michael Dugger]

Ken,

Thanks for the response. Robert is working on making the beam symmetries 
even better, so that we can get a good lock on the polarizations.

We will keep the FROST group informed as to what we find.

Take care,
Michael

On Mon, 8 Jan 2018, Ken Livingston wrote:

> 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
>> _______________________________________________
>> Frost mailing list
>> Frost at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/frost
>
>
> -- 
> =======================================================
> Ken Livingston
>
> Dept. of Physics & Astronomy,        Tel: +44 141 330 6428
> University of Glasgow,               Fax: +44 141 330 5889
> Glasgow G12 8QQ.
> Scotland. UK.
> =======================================================
>
>
> _______________________________________________
> Frost mailing list
> Frost at jlab.org
> https://mailman.jlab.org/mailman/listinfo/frost
>