What is the proton charge radius ?

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.