[PRad] [Fwd: New theoretical work on low-Q2 EM form factors]

[gasparan at jlab.org]

  Dear All,

 Take a look at this new work by Christian about theoretical construction
 for G_E.

 Ashot



---------------------------- Original Message ----------------------------
Subject: New theoretical work on low-Q2 EM form factors
From:    "Christian Weiss" <weiss at jlab.org>
Date:    Mon, October 23, 2017 12:06 pm
To:      "Ashot Gasparian" <gasparan at jlab.org>
         "Jose Manuel Alarcon Soriano" <alarcon at jlab.org>
--------------------------------------------------------------------------



Dear Ashot and Colleagues,


We just wanted to inform you of a recent theoretical work on low-Q2
nucleon EM
form factors that might be relevant for the planned PRad experiment,

  http://inspirehep.net/record/1631336

We calculate the low-Q2 FFs and their derivatives using a new method
combining
Chiral Effective Field Theory and dispersion analysis. The approach
incorporates
the exact analytic structure of the FF in t (position of singularities,
two-pion cut)
and allows us to compute the spacelike FFs at Q2 < 0.1 GeV^2 with
controlled accuracy.
In particular, we predict the values of the higher FF derivatives almost
model-independently
and show that they are of "unnatural" size, i.e., much larger than what
one would
estimate with a single-scale FF parametrization and the charge radius.
These findings should be directly relevant for the PRad analysis.


We would be happy to discuss with you these results and possible further
applications.
If you would like us to give a report at one of your collaboration
meetings, let us know.


Best regards,


   Ch. and Jose


-- 
Christian Weiss
Theory Center
Jefferson Lab
12000 Jefferson Ave
Newport News, VA 23606, USA
Phone: +1.757.269.7013
Fax:   +1.757.269.7002
E-mail: weiss at jlab.org