[Cuga] Pizza Seminar Series- Wednesday, April 20, 2011- A message from Hari Areti

[Lorelei Carlson]

Please RSVP to: lcarlson at jlab.org by COB on April 19, 2011.

Wednesday, April 20, 2011
****CC F113****
12:00-1:00pm

Nucleon Electromagnetic Form Factors
at Low Q^2 and the Proton Size Puzzle
  *Xiaohui Zhan*
Argonne National Laboratory

*Abstract:
*

The nucleon electromagnetic form factors are fundamental quantities 
which relate to the nucleon charge and magnetization distributions 
within the nucleon, and have been extensively measured through electron 
scattering in the last few decades. While the measurements on the proton 
form factors at large momentum transfer have provided information on the 
fine details of the proton structure and raised intense studies on the 
two-photon exchange effect, recent high precision polarization and cross 
section measurements in low Q^2 region have shown that the long-range 
structure is not as simple as previously believed. New value of the 
proton RMS charge radius is extracted based on updated world /ep/ 
scattering data at low Q^2 , and the result is consistent with other 
measurements based on electron-proton interactions. The combined results 
are 7.7? above the recent extraction from muonic hydrogen Lamb shift. 
This significant difference suggests either a problem with the 
extraction from muonic hydrogen, or else that something is missing in 
our understanding of the electromagnetic interaction


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