Approaches to high-density storage experiments with in-situ production and detection of ultracold neutrons

Low counting statistics is one of the most important challenges in modern experiments with ultracold neutrons (UCN). UCN densities in superthermal sources based on superfluid helium are normally much higher than those after UCN delivery to ex-situ volumes. Therefore, and due to the vanishing neutron absorption of 4 He, storage-based experiments performed in-situ promise significant sensitivity gains. Scalable measurements offer a promising path to simultaneously address the inefficient use of cold neutron beams as precursors for UCN production in 4 He, by recuperating the unused beam fraction, and confront the practical challenges of large-scale UCN infrastructure. We suggest strategies for the development of modular cryogenic cells, propose a novel approach for in-situ UCN detection, and discuss the ultimate statistical reach of such a multiplexed experiment for measuring the neutron’s permanent electric dipole moment (EDM). While dedicated research and development are needed to evaluate the feasibility for many requirements, a neutron EDM measurement with sensitivity well beyond 10 − 28 e cm seems possible. Such an experiment could be pursued at any compatible cold neutron beamline, e.g., at the Institut Laue–Langevin, or later using the ANNI facility or large beam port (LBP) at the European Spallation Source.