Search for a muon EDM using the frozen-spin technique

TL;DR

This paper proposes a high-sensitivity experiment using the frozen-spin technique to search for a muon electric dipole moment, potentially revealing new physics beyond the Standard Model.

Contribution

It introduces a novel experimental setup leveraging high electric and magnetic fields to significantly improve muon EDM sensitivity, utilizing existing and upcoming muon sources.

Findings

Projected sensitivity of σ(d_μ) ≤ 6×10^{-23} e·cm, three orders of magnitude better than current limits.

Potential to set new upper limits on muon EDM with existing muon fluxes.

Future improvements with high-intensity muon beams could further enhance sensitivity.

Abstract

This letter of intent proposes an experiment to search for an electric dipole moment of the muon based on the frozen-spin technique. We intend to exploit the high electric field, $E=1{\rm GV/m}$, experienced in the rest frame of the muon with a momentum of $p=125 {\rm MeV/}c$ when passing through a large magnetic field of $|\vec{B}|=3{\rm T}$. Current muon fluxes at the $\mu$E1 beam line permit an improved search with a sensitivity of $\sigma(d_\mu)\leq 6\times10^{-23}e{\rm cm}$, about three orders of magnitude more sensitivity than for the current upper limit of $|d_\mu|\leq1.8\times10^{-19}e{\rm cm}$\,(C.L. 95\%). With the advent of the new high intensity muon beam, HIMB, and the cold muon source, muCool, at PSI the sensitivity of the search could be further improved by tailoring a re-acceleration scheme to match the experiments injection phase space. While a null result would set a significantly improved upper limit on an otherwise un-constrained Wilson coefficient, the discovery of a muon EDM would corroborate the existence of physics beyond the Standard Model.