Description
The search for charged lepton flavor violating processes is an extremely powerful
tool for exploring new physics beyond the standard model of particle physics. The
MEGII experiment at the Paul Scherrer Institut in Switzerland aims at detecting
the lepton flavor violating μ → eγ decay by stopping positive muons in a very thin
target and measuring emitted photons and positrons with the best possible resolutions.
Photons are measured by a 2.7 ton ultra pure liquid xenon detector while positrons are
tracked in a specially designed gradient magnetic field by low material drift chambers
and are precisely timed by scintillation counters. A first phase of the experiment
(MEG) ended in 2016 excluding the existence of the decay with branching ratios larger
than 4.2 × 10−13 (90% C.L.). It provided approximately 30 times stronger constraints
on a variety of new physics models than previous experiments. MEGII will improve
the search sensitivity by another order of magnitude down to O(10−14) by upgrading
the detectors with up-to-date technologies. MEGII already started data taking in
2021 and continues increasing its statistics in the next 3-4 years to explore new physics
beyond the standard model from different angles than high energy collider experiments,
with a compatible or even higher sensitivity.