muEDM: Towards a Search for the Muon Electric Dipole Moment at PSI Using the Frozen-spin Technique

Abstract

The search for a permanent electric dipole moment (EDM) of the muon is an excellent probe for physics beyond the Standard Model of particle physics. We propose the first dedicated muon EDM search employing the frozen-spin technique at the Paul Scherrer Institute (PSI), Switzerland, with a sensitivity of 6 × 10 −23 e • cm, improving the current best limit set by the E821 experiment at Brookhaven National Laboratory by more than three orders of magnitude. In preparation for a high precision experiment to measure the muon EDM, several R&D studies have been performed at PSI: the characterisation of a possible beamline to host the experiment for the muon beam injection study and the measurement of the multiple Coulomb scattering of positrons in potential detector materials at low momenta for the positron tracking scheme development. This paper discusses experimental concepts and the current status of the muEDM experiment at PSI.

A large muon EDM from dark matter

“…In particular, the Future Circular Collider (FCC) may be able to measure κ µ with relative precision of ∼ 0.4% whose contours are shown as dot-dashed magenta lines in figure 3. 8 In the whole parameter region shown in the figure, the muon EDM is predicted to be larger than the future sensitivity of the PSI muEDM experiment, 6 × 10 −23 e cm [10][11][12]. The 2σ discrepancy of (g − 2) µ can be explained for 560 GeV < m ψ 1 < 780 GeV, while only the region of m ψ 1 m ϕ + 1 is favored for the correct DM relic density.…”

“…Table 1. Mass scales of new physics that produce the muon EDM at the one/two-loop level probed by the projected PSI muEDM experiment [10][11][12] (the Fermilab Muon g − 2 and J-PARC Muon g − 2/EDM experiments [8,9]) for each approach presented in the main text. Here, we assume λ ≈ 0.65 of around the weak coupling constant and y µτ ≈ 0.3 which is roughly the maximum value allowed by the measurement of the branching ratio of h → µτ (see, e.g., ref.…”

“…Table 1 shows mass scales of new physics that produce the muon EDM at the one/two-loop level probed by the projected PSI muEDM experiment [10][11][12] (the ongoing Fermilab Muon g − 2 experiment [8] and the future J-PARC Muon g − 2/EDM experiment [9]). Aside from the tuning approach, the table indicates that the radiative stability approach generates the largest muon EDM and its near-future measurements can probe mass scales larger than the TeV scale.…”

“…There is also a study on indirect bounds on the muon EDM by measuring EDMs of heavy atoms and molecules, which indicates |d µ | < 2 × 10 −20 e cm [7]. Moreover, the sensitivity to the muon EDM will be improved in the near future: the ongoing Fermilab Muon g − 2 experiments [8] and projected J-PARC Muon g − 2/EDM experiment [9] will explore the muon EDM at the level of 10 −21 e cm, while the Paul Scherrer Institute (PSI) muEDM experiment [10][11][12] will reach the sensitivity of 6 × 10 −23 e cm.…”

Minimal Inert Doublet benchmark for dark matter and the baryon asymmetry

“…Similarly, the current limit on the µEDM set by the muon (g − 2) experiment at Brookhaven National Laboratory and the projected ones by J-PARC and PSI muEDM are [68][69][70] |d BNL µ /e| < 1.9 • 10 −19 cm ≈ 9.6 • 10 −6 GeV −1 (2.9a)…”