LKB - Metrology of simple systems and fundamental tests

Charge Radius Experiment with Muonic Atoms

What is the proton size ?


R. Pohl et al.
Science 353, 669 (2016)

A. Antognini et al.
Science 339, 417 (2013)

R. Pohl et al.
Nature 446, 213 (2010)

The proton, which is one of the fundamental components of matter, could be smaller than it has been thought until now.This result has been obtained by the international collaboration CREMA in which the Metrology LKB team is involved. From spectroscopic measurements in muonic hydrogen, a value of the proton charge radius is deduced, which disagrees with the ones obtained by other methods. This result questions some predictions of Quantum Electrodynamics and could lead to re-evaluate the Rydberg constant.

The proton

Principle of the experiment on muonic hydrogen

Experimental set-up


Muonic helium spectroscopy