Monday, 25 November, 2013
National Institute of Standards and Technology
The Proton Radius Puzzle: An Unsolved Mystery
In July 2010, a paper in Nature reported a measurement made in Switzerland of the Lamb shift in muonic hydrogen, a negative muon bound to a proton, that may be considered a measurement of the proton radius. This value for the radius differs by seven standard deviations from the 2010 CODATA recommended value. The disagreement is a puzzle, and could conceivably turn out to be a fundamental shortcoming of quantum electrodynamics (QED). This would also be bad news for the fundamental constants, because many of the values rely on the assumption that the theory is correct.