Charged lepton flavour violation (cLFV) is suppressed beyond any experimental reach in the Standard Model of particle physics, thus its observation would clearly spots out the existence of physics beyond it. Muon properties, such as lifetime and mass, enable to construct very high intense and low energy 𝜇-beams to be then transported to a dedicated experimental apparatus and measure the emerging decay products. Among the muon decays under study, 𝜇→𝑒𝛾 and 𝜇→𝑒𝑒𝑒 are the most promising and the 𝜇 to e conversion in atomic nuclei complements them. The MEG II experiment at Paul Scherrer Institut searches for the 𝜇→𝑒𝛾 decay with a sensitivity of 6 10^(-14).
Despite the pandemic, the MEG II detector was assembled and commissioned in the last two years. I review the MEG II design and construction and then show the very first highlights of the current full engineering run towards the first physics data collection, expected in 2021.
In addition to the 𝜇→𝑒𝛾 other cLFV processes, such as 𝜇→ 𝑒X, 𝜇→𝑒𝛾𝛾 can be searched within the MEG II framework, an evaluation of the expected sensitivity will be discussed.
Beyond cLFV, MEG II will repeat the measurement of the 17 MeV X-boson resonance in Boron nuclear transitions which was reported by the Atomki collaboration; an improved sensitivity will be given by the new Cylindrical Drift Chamber. A dedicated data collection is expected in early 2022 during the main accelerator shutdown by using the MEG II CW accelerator.