Although a muon exists for only two millionths of a second, this is time enough for it to participate in many of the fundamental chemical processes available to stable charged particles. One can produce either positive or negative muons, and since they have a mass intermediate between that of the proton and the electron, it is not surprising that the positive muon tends to behave as if it were a light proton, while the negative muon behaves as if it were a heavy electron.

Muons

Muons (μ) are elementary particles of the lepton family which occur, transiently, as part of the natural decay scheme of pions (μ), as indicated by the overall sequence in Eq. [1.1].

Their origin and occurrence, therefore, require a source of pions. These are the lightest and commonest of the mesons, but they appear in nature extremely rarely, only when cosmic particles interact with the atmosphere. However, pions are readily created in one of three charge states (π+, π− or π∘) during high-energy nuclear collisions. This is because nuclear glue can be thought of as the exchange of ‘virtual’ pions between nucleons, so that the production of pions outside the nucleus can occur when a nuclear collision exceeds the rest mass of a pion (0.15 amu, or 140 MeV). Consequently, copious fluxes of pions are manufactured at targets in the beams of the world's several accelerators capable of producing protons at energies much greater than 140 MeV. When the short-lived positive or negative pion decays it creates an energetic muon of the same charge. The muon lives for 2.2 μS, on average, before decaying to an energetic electron of the same charge.