[Primex2] text from Sergey, [Fwd: silicon radius]

[gasparan at jlab.org]

  Dear PrimEx collaborators,

 For some reasons Sergey's recent email letter explaining the current
 status of the radius extraction from the PrimEx2 data set did not go
 to all of you. Here it is below, please take a look if you are
 interested.

 Ashot

---------------------------- Original Message ----------------------------
Subject: silicon radius
From:    gevs at jlab.org
Date:    Thu, September 1, 2016 9:38 am
To:      gasparan at jlab.org
Cc:      bernstn at mit.edu
--------------------------------------------------------------------------

Dear Colleagues,

In attachment I send you the classic  work done many years ago at DESY,
where authors have done the special investigation  of strong radius using
many nuclei.As a result they claim  that parameterization
 R=(1.12\pm 0.2)A^(1/3) for strong radius is the best one.
 At the end of their article (see Comments on the results) they discuss
the corrections from  approximations due to Glauber approach, which as
claim Aron can be essential  for light nuclei namely:
1) 1/A from taking exponents instead of polinoms
2) individual nucleon form factors have been ignored,which is
the same as our ignorance of exp(bt/2) in elementary amplitude
(we really take the nonflip amplitude f without this factor)
As  claimed in Comments these corrections can change their
parameterization  not more than 5% for A>27.
So if we believe to this work for silicon R=3.4fm and as I understand
such value fit silicon data well. From my point of view it is enough to
confined by this result for strong radius, which is widely exploited in
the literature.

I don't know the statement that electromagnetic and strong radius must be
the same so taking different radiuses we don't due mistake.
The reason why this radiuses can be different is ad separate issue which
can't be solved by one experiment even such precisious as our.
At least account of exponential dependence of elementary amplitude lets to
change in strong radius R^2=R_0^2+2b, where R_0 is radius for point like
nucleon and b is the slope in elementary amplitude.(Such renormalization
can be obtained only for Gauss parametrization of nuclear distribution and
neglecting absorption). Such correction is in 5-10% and is in the limits
of accuracy of parameter r_0 in parameterization.
As to the contribution of intermediate channel, for which we used factor 0.5
(which is in some sense arbitrary) one can take 0 or 1 for it to
understand what is its impact on the final result,

With kind regards Sergey




>   Barev Sergey,
>
>  Can you please spend some time and come up with a scientific explanation
>  of the larger radii from the coherent processes and what Aron is writing
>  in his note attached.
>
>  Thank you,
>  Ashot
>
>
>
>
> ---------------------------- Original Message ----------------------------
> Subject: [Primex2] radius increase in c12 and si28
> From:    "Yang Zhang" <yzhang132 at gmail.com>
> Date:    Wed, August 24, 2016 11:01 am
> To:      "primex2 at jlab.org" <primex2 at jlab.org>
> --------------------------------------------------------------------------
>
> Hi all,
>
> Professor Aron Bernstein provides an explanation to the radius increase.
> Please check it and let me know your thoughts. You can find it in the link
> below.
>
> AB-collab-23Aug16.pdf
> <https://www.jlab.org/primex/weekly_meetings/primexII/slides_2016_08_26/AB-collab-23Aug16.pdf>
>
> Best
>
> Yang
> _______________________________________________
> Primex2 mailing list
> Primex2 at jlab.org
> https://mailman.jlab.org/mailman/listinfo/primex2
>
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