[Mott] next meeting, Wed July 29th @ 1:30pm EST

[Xavier Roca Maza]

Dear all,

unfortunately, regarding self-energy corrections, I have little to add from
the last time we discussed (for those interested see explanation below).

Greetings,

Xavier

==============================================
Some theory explanations on the self energy corrections
(I have been confronting my view with Jakubassa-Amundsen):
==============================================

The big problem for the calculation of the self-energy correction is the
requirement that the electrons are dressed (i.e. eigenstates to the Coulomb
potential they are moving in), instead of simple plane waves. In addition,
the calculation of the self-energy requires also renormalization (that I do
not know how to do in our case): there are divergent integrals one should
deal with and, those, should be treated to properly "absorb" such
divergences.

Having said that, the only thing I can add now is what others have
calculated [Shabaev, Phys.Rev.A 61(2000)052112]. The calculations in this
work do not correspond exactly to what we need (quantitatively speaking),
although the corrections they calculate are analog to the calculations one
has to do in our case. So, I would expect an opposite sign for the two
contributions (vacuum polarization and self-energy) also in our case and
also the same order of magnitude. Then, if the latter is true in our case,
the QED corrections will amount to a 0.5% error (at most) in the Sherman
function at the kinematics and nuclei we are interested in.

May be at that point one should confront this with a QED expert?

Hope it is clear the problem...



2015-07-17 15:47 GMT+02:00 Joseph Grames <grames at jlab.org>:

> EGAD!  I meant 29th.  Wed July 29th!!!
>
> ----- Original Message -----
> From: "Joseph Grames" <grames at jlab.org>
> To: mott at jlab.org
> Sent: Friday, July 17, 2015 9:46:40 AM
> Subject: [Mott] next meeting, July 27th @ 1:30pm EST
>
> Let's meet again on Wed July 27th at 1:30pm EST in TL-2236.
>
> One or more of the efforts below could be discussed...
>
> 1. Dan - Based on three sets of runs (Run1, Marcy's calibration set, Joe's
> calibration set) determine elastic rate per detector vs. target thickness.
> Elastic rate means applying same cuts (fixed delta-time, then reasonable
> energy sigma) and normalizing to (time*intensity) product for the run
> groups, using either (both?) FADC or Scaler macro.  You can use both Lebow
> and FESEM target thickness, whichever makes sense.  Also, now that you've
> developed good tools can you extend your sensitivity studies of energy cuts
> (i.e. use same time cut) to look at ~1 sigma slices of asymmetry e.g. -2
> sigma to +4 sigma.  The question is:  how does asymmetry vary with slice?
> At this point you probably don't need to show us all the spectra, unless as
> an example, but focus on the summary plots.
>
> 2. Marcy - Based on the images we have (i.e. not planning to do more
> measurements) you are re-evaluating the FESEM image analysis to find the
> best way to quantify a systematic thickness and uncertainty from each image
> file, i.e. some of the limited number of images are better than others.
> The idea here is to compile a summary of the recipe used from start to end
> of process, and a table breaking out the systematics in a way which we can
> apply to all the foils.  Based on Dan's chi-square table posted ~recently
> suggests either measurement uncertainty ~somewhat underestimated (makes
> sense) or fit function not ideal (makes sense too).
>
> 3. Xavier - You are working on calculation the size of the self energy
> correction, the idea being that you are confident the vacuum polarization
> and self energy correction are of opposite, but may not cancel as well as
> speculated or suggested.
>
> 4. Marty - You are working on efficiently implementing -double scattering;
> we discussed meeting at JLAB or in DC to have a working meeting, map out
> options.  I'll be gone week of July 20th; can you suggest a date that would
> be convenient to do this...?
>
> 5. Joe - We are ~halfway through the summer shutdown.  The updated
> accelerator schedule suggests next window of opportunity would be in
> ~October; this gives us another 2-3 weeks beyond original period for Run
> 2.  We'll need to decide by middle of August what we might want to do in
> October.
>
> Joe
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>


-- 


Xavier Roca-Maza
Research Assistant Professor

Dipartimento di Fisica,        e-mail: xavier.roca.maza at mi.infn.it
Universita' degli Studi,        Phone: *+39-02-503-17290* (Office)
Via Celoria 16                    Fax: *+39-02-503-17-487*
20133 Milano (Italia)           Web page: http://www.mi.infn.it/~jroca/
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