Speaker
Description
The path to an “ultimate” nEDM apparatus is small measurement cells for suppressing systematic effects to a manageable level while achieving a sufficiently high ultracold neutron (UCN) density to improve statistical reach. The nEDM Superfluid technique offers this by exploiting a fortuitous combination of the properties of superfluid $^4$He, polarized $^3$He, and polarized UCN, allowing high UCN densities via superthermal production from cold neutrons, live in-situ UCN spin analysis, and comagnetometry. This yields reduced UCN transport and polarization losses and good systematic control. In particular, the false-EDM systematic is tunable via the strong temperature dependence of the $^3$He–phonon scattering mean free path. Other advantages include a large electric field (~75 kV/cm versus ~15 kV/cm in vacuum), superconducting magnetic shielding for suppressing field drifts over long precession times, and identical UCN production spectra in multiple cells. This technique is experimentally challenging. However, future efforts can leverage a decades-long base of R&D and potentially even "final" hardware. Should a modified geometry be desired, the technical know-how exists. With available cold neutron beams, a sensitivity of ~ $10^{-28}$ e.cm can be reached, providing the next major step for the field.
In this talk, the nEDM Superfluid technique will be reviewed, along with hardware availability. Efforts toward a demonstrator experiment at the ILL, a first step in a renewed European superfluid nEDM program, will be described. This experiment would demonstrate in-situ UCN production and detection of UCN-$^3$He capture scintillation light, and possibly in-situ UCN spin analysis via the unique double-free-precession light signal. Updates will also be given on the Systematic and Operational Studies (SOS) apparatus at NCSU/TUNL, whose pivotal measurement is the impact of $^3$He-phonon scattering on the motional correlation functions. Together, these two efforts form a strong launching pad for a full-scale experiment at the European Spallation Source using the E5 beamport, whose monolith insert is already installed.