Storage Ring to Search for Electric Dipole Moments of Charged Particles -- Feasibility Study

The proposed method exploits charged particles confined as a storage ring beam (proton, deuteron, possibly helium-3) to search for an intrinsic electric dipole moment (EDM) aligned along the particle spin axis. Statistical sensitivities could approach 10$^{-29}$ e$\cdot$cm. The challenge will be to reduce systematic errors to similar levels. The ring will be adjusted to preserve the spin polarisation, initially parallel to the particle velocity, for times in excess of 15 minutes. Large radial electric fields, acting through the EDM, will rotate the polarisation. The slow rise in the vertical polarisation component, detected through scattering from a target, signals the EDM. The project strategy is outlined. It foresees a step-wise plan, starting with ongoing COSY (Cooler Synchrotron, Forschungszentrum J\"ulich) activities that demonstrate technical feasibility. Achievements to date include reduced polarisation measurement errors, long horizontal-plane polarisation lifetimes, and control of the polarisation direction through feedback from the scattering measurements. The project continues with a proof-of-capability measurement (precursor experiment; first direct deuteron EDM measurement), an intermediate prototype ring (proof-of-principle; demonstrator for key technologies), and finally the high precision electric-field storage ring.