To measure the neutron electric dipole moment we must place a sample of neutrons in a uniform magnetic field and a strong electric field. The neutron spins will precess due their finite magnetic dipole moment
The electric dipole moment is determined by measuring a tiny difference in the precession frequency that is linearly dependent on the electric field strength.
The statistical sensitivity of an EDM experiment depends on the electric field (E), the number of neutrons (N) and the neutron storage time (τ): σ ∝ (E√Nτ
. The nEDM@SNS experimental approach, conceived by Golub and Lamoreaux
, takes advantage of an amazing confluence of superfluid helium properties to substantially increase E, N and τ:
A large density of ultracold neutrons (UCNs) can be produced through a superthermal process (8.9Å neutrons can be effectively 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.