Detailed Description

The statistical sensitivity (σ) of a neutron EDM measurement depends on the electric field (E), the number of neutrons (N) and the neutron storage time (τ):
$$\sigma\sim \frac{1}{E\tau\sqrt{N}}$$
The nEDM experiment at the Spallation Neutron Source is based on the concept discussed in R. Golub and S. K Lamoreaux, Physics Reports 237, 1-62 (1994). This approach takes advantage of an surprising confluence of superfluid helium properties to substantially increase E, N, and τ:

• A large density of ultracold neutrons (UCN) can be produced through a superthermal process (cold 8.9 angstrom neutrons are slowed by scattering off excitations in superfluid Helium).

• UCN can be stored in a material bottle with wall-loss times longer than their decay lifetime.

• Superfluid Helium can support strong electric fields.

• Spin-polarized ³He 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-³He capture reaction.