A Measurement of the Muon Magnetic Moment Using Cosmic Rays

Abstract

The muon magnetic moment was measured via the decay of polarized cosmic-ray muons in a constant magnetic field with a three-scintillator detector system. Cosmic-ray muons stop in the central detector, precess in the magnetic field, and then decay by emitting positrons along the muon spin axis. A quantum-mechanical calculation allows the g-factor to be extracted from a measurement of the number of positrons emitted into one direction as a function of decay time. The results are t = 2.28 ± 0.07 µs (mean decay time) and g = 2.74 ± 0.20. Some possible explanations for the large value of g are discussed.