[Halld-tagger] Fwd: polarization update

Mon Mar 14 08:34:17 EDT 2016

Hi Everyone -

  I just wanted to comment that there has been spectacular progress on all fronts in
understanding the degree of linear polarization. Everyone involved has done a 
fantastic job in getting preliminary results out as quickly as possible, and the entire 
collaboration is thrilled to see that within errors, all the methods that we have report
consistent (preliminary) results. We now know that our diamonds are producing 
coherent bremsstrahlung and appear quite consistent with our predictions. This
work is something we should all be very proud of.

   We also fully understand that none of these results are final. But the fact that people
are able to get us preliminary results is crucial to our moving forward. I also feel that
without the apparent redundancy that we have, most of us would not be nearly as 
comfortable as we are now.

   Curtis
---------
Curtis A. Meyer			MCS Associate Dean for Faculty and Graduate Affairs
Wean:    (412) 268-2745	Professor of Physics
Doherty: (412) 268-3090	Carnegie Mellon University
Fax:         (412) 681-0648	Pittsburgh, PA 15213
curtis.meyer at cmu.edu	http://www.curtismeyer.com/

> On Mar 14, 2016, at 8:17 AM, Nathan Sparks <nsparks at jlab.org> wrote:
> 
> The reported degree of polarization from the TPOL is a rough estimate, based on the information I had available at the time.
> I have no reason to believe it is not in the right ballpark, and it was not presented as a final result.
> 
> -Nathan
>> On Mar 14, 2016, at 7:48 AM, dugger at jlab.org wrote:
>> 
>> Hi,
>> 
>> The reported polarizations for the polarimeter are not correct. It was too
>> early for the degree of polarization to have been reported.
>> 
>> Take care,
>> Michael
>> 
>>> Message from Ken regarding comparison between different methods for beam
>>> polarization estimation.
>>> -forwarded by Richard Jones
>>> 
>>> ---------- Forwarded message ----------
>>> From: Ken Livingston <Kenneth.Livingston at glasgow.ac.uk>
>>> Date: Mon, Mar 14, 2016 at 6:35 AM
>>> Subject: Re: polarization update
>>> To: Justin Stevens <jrsteven at jlab.org>, Nathan Sparks <nsparks at jlab.org>,
>>> Richard Jones <richard.t.jones at uconn.edu>
>>> 
>>> 
>>> Hi Justin,
>>> 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.
>>> 
>>> 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).
>>> 
>>> It looks like both your studies are assuming that Ppara = Pperp.
>>> 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.
>>> 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.
>>> 
>>> 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.
>>> 
>>> I'll need to scrutinise it as soon as I get time.
>>> 
>>> 
>>> Regards,
>>> Ken
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> On 11/03/16 17:06, Justin Stevens wrote:
>>> 
>>>> FYI, from this mornings meeting: rho and TPOL asymmetries comparing 20
>>>> and
>>>> 50 um diamonds.
>>>> 
>>>> https://logbooks.jlab.org/entry/3390212
>>>> https://logbooks.jlab.org/entry/3390218
>>>> 
>>> 
>>> 
>>> --
>>> =======================================================
>>> Ken Livingston
>>> 
>>> Dept. of Physics & Astronomy,        Tel: +44 141 330 6428
>>> University of Glasgow,               Fax: +44 141 330 5889
>>> Glasgow G12 8QQ.
>>> Scotland. UK.
>>> =======================================================
>>> _______________________________________________
>>> Halld-tagger mailing list
>>> Halld-tagger at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/halld-tagger
>> 
>> 
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