Charged Lepton Flavour Violation: An Experimental and Theoretical Introduction

TL;DR

This paper provides a comprehensive overview of charged lepton flavour violation, discussing theoretical motivations and experimental efforts, including recent limits set by the MEG experiment and future planned searches.

Contribution

It offers a pedagogical introduction to the theoretical background and experimental techniques for charged lepton flavour violation searches, highlighting recent results and future prospects.

Findings

MEG set the best limit on $oldsymbol{ ext{mu} o e ext{gamma}}$ decay

No positive evidence of charged lepton flavour violation found so far

Upcoming experiments aim for unprecedented sensitivity in multiple channels

Abstract

Charged lepton flavour violating transitions would be a clear signal of new physics beyond the Standard Model. Their search has been carried out in a variety of channels, the most sensitive being those involving a muon: however no positive evidence has been found so far. The MEG experiment has recently set the best limit on such processes by investigating the existence of the $\mu \to e\gamma$ decay. In the next decade several experiments are planned to pursue the search for $\mu \to e\gamma$, $\mu \to eee$, $\mu \to e$ conversion in nuclei, as well as on processes involving the $\tau$, to an unprecedented level of precision. In this review we want to give a pedagogical introduction on the theoretical motivations for such searches as well as on the experimental aspects upon which they are based.