This paper investigates the electromagnetic interactions of muons. The various processes such as knock‐on electron‐, bremsstrahlung‐, direct electron pair production, and nuclear interactions are described in detail. The energy range concerned extends from 109 eV up to 1015 eV for primary muons and from 108 eV up to 1014 eV for energy transfers to the secondaries.
On the one hand the measurement of muon interactions represents a test of quantum electrodynamics. On the other hand the high energies available in cosmic rays would possibly lead to the measurement of new processes or the detection of new particles. One hopes to find in the high energy domain the answer to the question why the muon exists at all and if there are properties (apart from differences in mass, lifetime, and lepton number) which distinguish it from a mere heavy electron.
The different experimental techniques are described and the various experimental results on muon interactions are presented and compared with relevant QED‐theories.
Observed deviations between theory and experiment and anomalies in muon interactions are critically investigated and discussed in the light of experimental difficulties and interpretation problems. In general, agreement between theory and experiment is found, i.e. QED‐theories describe the results adequately. However, some experiments claim to have detected anomalies in muon physics in the cosmic ray beam. But the hypotheses on new processes and new particles in the high energy range do not withstand a critical analysis. It is concluded that the observed deviations can be understood in the framework of conventional theories.
