Abstract

Flavour-changing transitions of charged leptons have been a topic of experimental investigation since the early days of particle physics, and this helped shape some of the basic laws that any successful model of particle physics would have to obey, including what we now call the Standard Model.

While such phenomena have never been observed to date, when the discovery of neutrino masses and oscillations broke the Standard Model, it transformed the question “Does charged lepton flavour violation exist?” into “How much?” and “How?”, and even “Why haven’t we seen it yet?”.

In this seminar, I will describe the current experimental and theoretical state of the field, and why the next generation of experiments could hold the keys that lead the way to a fuller understanding of our universe, offering complementary discoveries that experiments at the high-energy frontier cannot reach.

I will then focus on muon-to-electron conversion experimentation, and specifically the COMET /PRISM programme which is promising a sensitivity improvement of four orders of magnitude compared to the current record, potentially improving to six orders, which could open the path to precision measurements with multiple lepton flavour-violating probes of Physics Beyond the Standard Model.