The Mu2e Experiment

The Mu2e experiment at Fermilab will search for new phenomena by measuring the rate of muon to electron conversion in the field of a nucleus, μN → eN. Data collection will begin in 2021 and will continue for three years. The experiment will achieve a single-event sensitivity of 3 × 10⁻¹⁷ with < 0.5 background events. This equates to an experimental limit on the conversion rate of 8 × 10⁻¹⁷ at the 90%CL, which is a four-order-of-magnitude improvement over existing limits. A pulsed proton beam will be provided by the Fermilab booster, and a three-part solenoid will be used to produce, transport, and stop a muon beam on an Al target, whereafter the muons may interact and undergo conversion. The sensitivity requires that 10¹⁸ muons be stopped, which calls for the most intense muon beam ever made. The background requirement sets a strong constraint on the momentum resolution, which translates into stringent demands on detector performance. The major detectors consist of a precision, ultra low-mass straw-tube tracker, used for momentum reconstruction; a crystal calorimeter for enhanced PID; and an encasing multi-layer set of scintillation counters to veto false signals otherwise generated by cosmic muons. (paper)