Improved Indirect Limits on Muon Electric Dipole Moment

Area of Science:

• Particle Physics
• Atomic and Molecular Physics
• Quantum Electrodynamics

Background:

• The muon g-2 experiment shows a persistent discrepancy with the Standard Model.
• Future experiments aim to measure the muon electric dipole moment (EDM), d_μ.
• Existing EDM measurements in heavy systems can provide indirect constraints on d_μ.

Purpose of the Study:

• To assess the indirect constraints on the muon EDM (d_μ) from heavy atom and molecule EDM measurements.
• To investigate the dominant muon EDM effects arising from muon-loop induced CP-odd amplitudes near large nuclei.
• To compute the d_μ-induced Schiff moment in Mercury-199 and CP-odd effects in ThO.

Main Methods:

• Calculated the d_μ-induced Schiff moment for the ^{199}Hg nucleus.
• Determined the relevant combination of electron EDM (d_e) and semileptonic C_S operator for CP-odd effects in ThO.
• Analyzed the muon-loop induced "light-by-light" CP-odd amplitude.

Main Results:

• Derived indirect constraints: d_μ(^{199}Hg) < 6 × 10⁻²⁰ e·cm.
• Derived indirect constraints: d_μ(ThO) < 2 × 10⁻²⁰ e·cm.
• These limits represent a threefold and ninefold improvement over the Brookhaven National Laboratory muon beam experiment.

Conclusions:

• EDM measurements in heavy atoms and molecules provide significant indirect constraints on the muon EDM.
• The derived limits on d_μ are more stringent than those from previous muon beam experiments.
• These findings are crucial for interpreting future dedicated muon EDM measurements.