The Mu2e experiment, under construction at Fermilab will search for the neutrinoless coherent conversion of the muon into an electron in an aluminum nucleus. This Charged Lepton Flavor Violation (CLFV) process has a very clear signature, a single monoenergetic electron with energy slightly below the muon rest mass. The Mu2e experiment aims to improve by four order of magnitude the current best limit on the ratio (Rμe) between the conversion and muon capture rates and reach a single event sensitivity of 3 x 10-17 on Rue.
Another important physics goal would be that of searching for a Lepton Number Violation (LNV) process. Neutrinoless double beta decay (0) has set the most stringent limit on this kind of process. The conversion of stopped negative muons to positrons in the field of a nucleus, −+(,)→ e++(,−2), is an example of both CLFV and LNV. This μ- à e+ conversion is important because some models estimate that this type of process can occur at much higher rates than the LNV process.
The experiment goal on Rμe is obtained with a very intense, pulsed, negative muon beam sent to an aluminum target for a total number of 1018 stopped muons in three years of running. The production and transport of the muons is achieved with a sophisticated magnetic system composed of a production, a transport and a detector solenoid; the latter one contains the aluminum stopping target followed by a Straw-tube Tracker and a Crystal Calorimeter. The entire detector region is surrounded by a Cosmic Ray Veto system.
Mu2e is under design and construction at the Muon Campus of Fermilab. In the current schedule, the experiment start is foreseen for 2023 followed by 3 years of data-taking.