<div dir="ltr">Message from Ken regarding comparison between different methods for beam polarization estimation.<div>-forwarded by Richard Jones</div><div><br><div class="gmail_quote">---------- Forwarded message ----------<br>From: <b class="gmail_sendername">Ken Livingston</b> <span dir="ltr"><<a href="mailto:Kenneth.Livingston@glasgow.ac.uk">Kenneth.Livingston@glasgow.ac.uk</a>></span><br>Date: Mon, Mar 14, 2016 at 6:35 AM<br>Subject: Re: polarization update<br>To: Justin Stevens <<a href="mailto:jrsteven@jlab.org">jrsteven@jlab.org</a>>, Nathan Sparks <<a href="mailto:nsparks@jlab.org">nsparks@jlab.org</a>>, Richard Jones <<a href="mailto:richard.t.jones@uconn.edu">richard.t.jones@uconn.edu</a>><br><br><br>Hi Justin,<br>
That a very nice study. It's exactly what's needed. If we believe the photon asymmetry for the rho in this energy range is really 1, and are convinced that it's very cleanly extracted signal, that's the best polarimiter we can have. It has an event rate that's better than the triple polarimiter and doesn't need an analysing power, and it does not need all the vaguely known parameters that are required to match the enhancement with a coherent brem calculation.<br>
<br>
For the 20 um radiator it's also good to see that, as we'd expect, the shape of the enhancement (and hence polarization) is much better with collimated data rather than raw scalers. The similarity between the polarization for the 20um and 50um is borne out by Nathan's studies although the energy range is different (8-9GeV).<br>
<br>
It looks like both your studies are assuming that Ppara = Pperp.<br>
I got the impression from the raw spectra that this might not be true for the 20um diamond. It would be good to check this out.<br>
A quick and check would come from using the more complicated fit function I sent you earlier, where the flux ratio and pol ratio are free parameters. >From this, you could plot the pol ratio as a function of E_gammma, as you have for Sigma.<br>
<br>
My "phenomenological fit" is clearly not as phenomenal as I'd hoped. It doesn't cope with the ~200MeV spread in the coherent edge for the 20um diamond. I believed it would. It can fit almost any enhancement, but is not much use if it doesn't get the corresponsing polarization correct. Either I've made a silly assumption somewhere, screwed up the algebra or screwed up the code. Maybe all three together - although it generally gives good agreement when used to extract asymmetries and compare with previous measurements.<br>
<br>
I'll need to scrutinise it as soon as I get time.<br>
<br>
<br>
Regards,<br>
Ken<div class="HOEnZb"><div class="h5"><br>
<br>
<br>
<br>
<br>
<br>
<br>
On 11/03/16 17:06, Justin Stevens wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
FYI, from this mornings meeting: rho and TPOL asymmetries comparing 20 and 50 um diamonds.<br>
<br>
<a href="https://logbooks.jlab.org/entry/3390212" rel="noreferrer" target="_blank">https://logbooks.jlab.org/entry/3390212</a><br>
<a href="https://logbooks.jlab.org/entry/3390218" rel="noreferrer" target="_blank">https://logbooks.jlab.org/entry/3390218</a><br>
</blockquote>
<br>
<br></div></div><span class="HOEnZb"><font color="#888888">
-- <br>
=======================================================<br>
Ken Livingston<br>
<br>
Dept. of Physics & Astronomy, Tel: <a href="tel:%2B44%20141%20330%206428" value="+441413306428" target="_blank">+44 141 330 6428</a><br>
University of Glasgow, Fax: <a href="tel:%2B44%20141%20330%205889" value="+441413305889" target="_blank">+44 141 330 5889</a><br>
Glasgow G12 8QQ.<br>
Scotland. UK.<br>
=======================================================<br>
<br>
</font></span></div><br></div></div>