Speaker
Randolf Pohl
(Max-Planck-Institut für Quantenoptik)
Description
The charge radius Rp of the proton has so far been known only with a precision of about 1% from both electron scattering and precision spectroscopy of hydrogen.
We have recently determined Rp by means of laser spectroscopy of the exotic "muonic hydrogen" atom [1]. Here, the muon, which is the 200 times heavier cousin of the electron, orbits the proton with a 200 times smaller Bohr radius. This enhances the sensitivity to the proton's finite size tremendously.
Our new value Rp = 0.84184 (67) fm is ten times more precise than the generally accepted CODATA value, but it differs by 5 standard deviations from it. A lively discussion about possible solutions to the "proton size puzzle" has started.
[1] R. Pohl, A. Antognini, F. Nez et al. (CREMA collaboration),
"The size of the proton", Nature 466, 213 (July 2010)
Primary author
Randolf Pohl
(Max-Planck-Institut für Quantenoptik)
