Muon to electron conversion search in the presence of Al nuclei at the Fermilab Mu2e experiment: Motivation, Design and Progress

Abstract

The Mu2e experiment aims to find charged lepton flavor violation(CLFV) by measuring the monochromatic electrons from µ − N → e − N conversion with an unprecedented single event sensitivity of 3 × 10 −17. When completed, the experiment will improve the current limit by four orders of magnitude and make a previously unexplored phase space available for the search for beyond the standard model physics. Physics motivation for the experiment is discussed and design choices for the detectors and various sub systems are explained in this document. The construction of the Mu2e experiment is well underway and commissioning will begin in late 2022 with first data taking in late 2025 and 4-5 years of data taking thereafter to reach our goal.

Leptonic CP violation from a vector-like lepton

“…In the future, the Mu2e experiment [51,52] is expected to dramatically improve the limit to the one in (5.14). This limit can be written in terms of k as…”

“…giving us the strongest constraint on this quantity. The future Mu2e [51,52] and COMET [53,54] experiments are expected to dramatically improve the constraint and reach Γ conv µ→e /Γ capt Al < 3 × 10 −17 using aluminium nuclei. Given the different nucleus, we can use the estimate shown in refs.…”

Isotope dependence of muon-to-electron conversion

“…It is particularly sensitive to effective LFV operators involving quarks [3,4]. New experiments DeeMe [5,6], COMET [7,8], and Mu2e [9,10] are under development and they are expected to improve the existing limits on the conversion rate by several orders of magnitude. While the conversion searches target New Physics discovery, it is possible to differentiate between different LFV effective operators using complementary target nuclei in the event of a positive signal observation using the µ − → e − conversion rate dependence on the target nucleus (notably its charge Z), [4,[11][12][13][14][15].…”

Isotope dependence of muon decay in orbit

“…Particularly clean processes are the decays µ → eγ and µ → 3e as well as the coherent µ − → e − conversion in the field of a nucleus, µ − +(A, Z) → e − +(A, Z), the latter being especially sensitive to effective LFV operators involving quarks [2,3]. An immense jump in sensitivity to µ − → e − conversion in nuclei is expected in the near future with experiments such as DeeMe [4,5], COMET [6,7], and Mu2e [8,9]. Since the µ − → e − conversion rate depends on the target nucleus (notably its charge Z), it is possible to differentiate between different LFV effective operators using complementary target nuclei in the event of a positive signal observation [3,[10][11][12][13][14].…”