DATE: 2016 Nov. 1st. 16:00-17:00
PLACE: ASRC Bldg.
TITLE:Precision determination of the proton charge radius
by elastic electron scattering at an ultra-low Q2 region
LANGUAGE: English
SPEAKER: Prof. Toshimi Suda (Tohoku University)
CONTACT: Dr. Kazuya Aoki, j-parc-pn-seminar-(AT)-ml.post.kek.jp
Abstract:
The sizable difference of the proton charge radius
derived from electron scattering and the Lamb-shift measurement of muonic
hydrogen caused a considerable confusion in our community, and triggered
intensive discussions about its possible reasons. The problem is not yet
settled even today, and it is called as “Proton Radius Puzzle”.
In the seminar, I will discuss our project of electron scattering
experiments off proton using a 60 MeV electron linac of Tohoku University.
Elastic electron-scattering cross section will be measured in the lowest-ever
momentum transfer region, Q2 = 0.0003 - 0.005 (GeV/c)2, and the charge
form factor, GE(Q2), is extracted by using the Rosenbluth separation technique.
Since the charge radius is defined as a derivative of GE(Q2) at Q2 = 0,
this project will provide the least model-dependent proton charge radius
ever determined by electron scattering, which will be crucial to understand
the puzzle. Such study including the Rosenbluth separation needs an energy-variable
low-energy electron accelerator, and our “old“ low-energy electron linac of Tohoku University
just fits the purpose.
In my talk, I will firstly review “Proton Radius Puzzle” and discuss the experimental methods so far
employed to determine the proton charge radius. Then I will discuss the details
of our project which is now underway at Tohoku University.