MEG II and Muon CLFV programs at PSI

We report a search for the charged lepton flavor-violating decay 𝜇→𝑒𝛾 using the MEG II dataset collected in 2021 – 2022. The sensitivity of this search was 2.2 ×10−13, improving upon the

previous result by a factor of 2.4. No excess over the expected background was observed, and we set a new 90 % C.L. upper limit on the branching ratio of 1.5 ×10−13. The sensitivity remains statistically limited, and with additional data and improved analysis methods, the experiment aims to reach its ultimate goal of6 ×10−14. This talk mainly focuses on the status of the MEG II experiment.

In addition, other experimental programs searching for charged lepton flavor violation are running at PSI: the Mu3e experiment searching for 𝜇→𝑒𝑒𝑒 and a future experiment to search for 𝜇→𝑒𝛾 at an order of magnitude higher sensitivity. The Mu3e experiment started its engineering run in 2025, and performance evaluation and analysis are ongoing. The future 𝜇→𝑒𝛾 experiment aims for an order of magnitude higher sensitivity than the MEG II, and simulation studies and detector R&D are ongoing. This talk presents the status of these programs.