Improved measurement of the permanent electric dipole moment of the Xe-129 atom

• Applicant: Dr. Fabian Allmendinger
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569350435

The Standard Model (SM) of particle physics is structurally complete and highly successful in describing fundamental interactions but fails to fully explain key phenomena, particularly the observed baryon asymmetry of the Universe. Theoretical models predict a much smaller baryon-to-photon density ratio than observed, necessitating additional CP violation beyond the SM. One promising approach to investigating new CP violation sources is precision measurements of permanent electric dipole moments (EDMs) of fundamental or composite particles. Experiments on electrons, neutrons, atoms, and molecules have set stringent constraints on CP-violating interactions. Measurements on different systems are required to distinguish between various EDM contributions. Recent global analyses of EDM constraints highlight the need for improved precision measurements to refine the parameter space for new physics models. The project’s primary objective is to improve the current 129Xe EDM sensitivity of 1.5 ⋅ 10-27 ecm (95% CL) by a factor of 15, targeting a precision of 1.0 ⋅ 10-28 ecm (95% CL). This will further constrain hadronic and electron-nucleon CP-violating interactions, to which diamagnetic atoms such as 129Xe are particularly sensitive. Several critical experimental enhancements have already been implemented, including a new magnetically shielded room (MSR), which provides an electromagnetically low-noise environment and, due to low field gradients (~1 pT/cm), enables long spin coherence times. These improvements are expected to enhance measurement sensitivity by reducing noise levels from 10 to 1 fT/√Hz and allowing fo higher 129Xe gas pressures without sacrificing spin coherence time. A secondary objective is to establish a foundation for future high-precision EDM measurements, ultimately reaching sensitivities of <1.0⋅10-29 ecm (95% CL), comparable to the 199Hg EDM limit. The planned experiments will take place within a larger research collaboration that includes groups working on neutron and 199Hg EDM experiments. Synergy effects from the shared measurement principle of co-magnetometry will be leveraged to significantly improve systematic measurement uncertainties. A crucial step toward this long-term goal is the commissioning of an improved EDM cell designed to sustain higher electric fields while minimizing systematic effects. By advancing the sensitivity of 129Xe EDM measurements, this project aims to place stringent new constraints on CP violation, contributing to the broader effort of uncovering new physics beyond the Standard Model.

• DFG Programme: Research Grants