Limits on the permanent electric dipole moment of ¹²⁹Xe

Any precise value of a CP-violating electric dipole moment (EDM) on a fundamental particle has large impact on the Standard Model (SM). In case its value is larger than predicted by SM it would be direct evidence of New Physics. This has lead to a considerable number of experiments on particles, atoms, molecules and condensed matter systems. These approaches differ substantially in their intrinsic sensitivity and associated systematic uncertainties. We focus on conceptually different experimental implementation with an emphasis on the differences in sensitivity and characteristic time scales of the experiments. One approach exploits molecules such as barium monofluoride (BaF) which offer large intrinsic enhancement factors for a potential electron EDM and has typical coherence times of several 10ms. This experiment is currently set up at the University of Groningen. A different approach is utilizing spin precession of polarized noble gases, which is sensitive in particular to nuclear EDMs. Here coherence times are of order 10³ s.

The MIXed collaboration (University of Heidelberg, GER, University of Mainz, GER, FZ Jülich, GER and University of Groningen, NL) has performed a measurement campaign on a gas mixture of spin-polarized ³He (co-magnetometer) and ¹²⁹Xe in a 10cm diameter spherical glass cell. The experiment is performed in a magnetically shielded room at Forschungszentrum Jülich and it uses a guiding magnetic field of 400nT. The preliminary results on the EDM in the ¹²⁹Xe of these measurements will be presented which exceed the existing present limits.