Precise measurement of the Fermi-coupling constant Precise Measurement of μ+ Lifetime

The Fermi coupling constant (GF) is one of the most basic parameters of the Standard Model and its accuracy is limited by the uncertainty of the μ+ lifetime. However, its accuracy has not been improved in more than a decade. Recently, its importance was recognized again and an experiment with a new experimental technique started at the RIKEN-RAL Muon Facility and similar experiments are proposed at PSI. A possibility to improve the experiment with a future muon source is discussed.