Motional spin relaxation in large electric fields

We discuss the precession of spin-polarized ultracold neutrons (UCNs) and He3 atoms in uniform and static magnetic and electric fields and calculate the spin relaxation effects from motional v×E magnetic fields. Particle motion in an electric field creates a motional v×E magnetic field, which when combined with collisions produces variations of the total magnetic field and results in spin relaxation of neutron and He3 samples. The spin relaxation times T1 (longitudinal) and T2 (transverse) of spin-polarized UCNs and He3 atoms are important considerations in a new search for the neutron electric dipole moment at the Spallation Neutron Source nEDM experiment. We use a Monte Carlo approach to simulate the relaxation of spins due to the motional v×E field for UCNs and for He3 atoms at temperatures below 600 mK. We find the relaxation times for the neutron due to the v×E effect to be long compared to the neutron lifetime, while the He3 relaxation times may be important for the nEDM experiment.