Precise muon lifetime measurement at the RIKEN-RAL muon facility and prospects at a high intense muon source

Fermi coupling constant (GF) which is one of the most important parameter in the Standard Model, can be determined by measuring the positive muon lifetime (τμ+). However, its accuracy has not been improved for 15 years. We proposed a new method at the RIKEN-RAL muon facility, called ‘multi-decay per one time window’ in order to realize a higher event rate with a multi-segmented detector to reduce the pile-up effect. umulated ∼1010 muon decay events and the analysis is in progress to achieve 10 ppm accuracy. The exponential decay law was tested for the muon decay at the same time and the preliminary upper-limit was obtained. Future lifetime measurement with the high intense muon source is also discussed.