Precision Measurements on the Muon, Muonium, Positronium, and Helium as Related to the Fundamental Atomic Constants

Abstract

Quantum electrodynamics is our best understood and most precisely verified theory. Both the electron and the muon appear to be Dirac particles with conventional electrodynamic coupling. Electrons and muons partake in no strong interactions but they do have weak interactions. Precise measurements on these particles, both when free and when in the bound hydrogen-like systems of muonium (μ+ e−) and positronium (e+ e−) have been vital to the establishment and verification of the theory of quantum electrodynamics. Such measurements are also useful for obtaining information about certain of the fundamental atomic constants. For the interpretation of these measurements only the electromagnetic interactions need be considered because the weak interactions are small by comparison. The effects of strongly interacting particles on higher order radiative corrections become important1 only to an accuracy well beyond present experimental precision. In contrast, the effect of strong interactions on the hydrogen atom, which contains a proton, is considerably greater than the uncertainties of present-day experiments.