1. Proton Radius Extraction From State-of-the-Art Theory
Jose M. Alarcón, Douglas W. Higinbotham, Christian Weiss, and Zhihong Ye
Phys. Rev. C 99 (2019) ;
Figure by APS/Alan Stonebraker

2. Definition of the Proton Radius
This definition is consistent with the definition of the radius being used by the atomic and mounic Lamb shift measurements.
Gerald A. Miller, Phys. Rev. C 99 (2019)
For electron scattering the problem is that we don’t measure at Q2 of zero.
See Weizhi Xiong’s 5:20 pm on how PRad will improve the situation by measuring from extremely low to moderate Q2
Douglas W. Higinbotham (Jefferson Lab)

3. Is There Some Way To Avoid The Extrapolations?!
Recent Global Fit
Z. Ye et al., Phys. Lett. B 777 (2018) 8.
Used world data
Fixed the Radius to the CODATA-2014 value
Recent Theory Work
Jose Alarcon and Christian Weiss, Phys. Lett. B 784 (2018)
Dispersively Improved Chiral Effective Theory
Proper analytic behavior of the Form Factors
Work was Expanded In Radius (i.e. the radius is there unknown parameter).
Douglas W. Higinbotham (Jefferson Lab)

4. Douglas W. Higinbotham (Jefferson Lab)
The Goldilocks Method
Take the global fit and simply fix the radius to different values
Values 0.80 to 0.90 fm (completely did the regression for each radius)
Different radii slightly change the normalizations of the data.
Done in the back room of the counting house while waiting for beam.
Asked Alarcon & Weiss to fix the radius to different values in their model.
Generated many different curves for different radii
Each curves has all the proper physical properties.
Compare
Is there a curve where the global fit and the theory agree? (i.e. is there a just right?)
If so, what is the radius of that curve?
Douglas W. Higinbotham (Jefferson Lab)

5. Douglas W. Higinbotham (Jefferson Lab)

6. Douglas W. Higinbotham (Jefferson Lab)
Summary and Outlook
Dispersively Improved Chiral Effective Field Theory is consistent with a proton charge radius of 0.844(7) fm (published 5 April 2019) :
Disagrees with CODATA-2014: Proton Radius (61) fm
Agrees with CODATA-2018: Proton Radius (19) fm (announced 20 May 2019)
PRad results to be discussed this afternoon ( Weizhi 5:20 pm )
And many more results coming soon including new atomic Lamb results
And when you have a nice JLab related result please talk to Kandice Carter!
Let her know when major new result is going to be announced or published
Also let know if you have a result has interesting or easy to tell story.
Douglas W. Higinbotham (Jefferson Lab)

7. Douglas W. Higinbotham (Jefferson Lab)
Results in case the animation isn’t working or presentation has been turned into a pdf file.
Douglas W. Higinbotham (Jefferson Lab)