Experimental Searches for Muon to Electron Conversion in Nuclei

Abstract

Charged lepton flavor violation (CLFV) provides a highly sensitive probe of physics beyond the Standard Model. This experimental review discusses $μ^{-} \to e^{-}$ conversion in nuclei, which is a muon CLFV process characterized by a clean monoenergetic-electron signature and the ability to exploit large samples of stopped muons. It describes the physics motivation, basic experimental principles, key background sources, and search strategies, as well as the status and prospects of past and next-generation experiments such as COMET and Mu2e. Future experimental concepts may extend the sensitivity even further. If a signal is observed, comparisons among results obtained with different target nuclei and with those from complementary searches for other muon CLFV decay modes will be essential for identifying the underlying interaction.