The statistical sensitivity (sigma) of an EDM experiment depends on the electric field (E), the number of neutrons (N) and the neutron storage time (tau):
sigma ~ 1 / (E * sqrt(N*tau))
The nEDM experiment at the Spallation Neutron Source was conceived by Golub and Lamoreaux in a seminal paper. This approach takes advantage of an amazing confluence of superfluid helium properties to substantially increase E, N, and tau:
• A large density of ultracold neutrons (UCNs) can be produced through a superthermal process (8.9 angstrom neutrons are stopped by scattering off excitations in superfluid Helium).
• UCNs can be stored in a material bottle for times longer than their decay lifetime.
• Superfluid Helium can support strong electric fields.
Furthermore, spin-polarized Helium-3 can be used as a co-magnetometer (to minimize and control systematic errors associated with non-zero magnetic field gradients), and as a spin analyzer, producing scintillation light (signal) in response to the spin-dependent n-Helium-3 capture reaction.