Motional Spin Relaxation in Large Electric Fields

Abstract

We discuss the precession of spin-polarized Ultra Cold Neutrons (UCN) and ${}^3$He atoms in uniform and static magnetic and electric fields and calculate the spin relaxation effects from motional $v\times E$ magnetic fields. Particle motion in an electric field creates a motional $v\times E$ magnetic field, which when combined with collisions, produces variations of the total magnetic field and results in spin relaxation of neutron and ${}^3$He samples. The spin relaxation times $T_1$ (longitudinal) and $T_2$ (transverse) of spin-polarized UCN and ${}^3$He atoms are important considerations in a new search for the neutron Electric Dipole Moment at the SNS \emph{nEDM} experiment. We use a Monte Carlo approach to simulate the relaxation of spins due to the motional $v\times E$ field for UCN and for ${}^3$He atoms at temperatures below $600,\mathrm{mK}$. We find the relaxation times for the neutron due to the $v\times E$ effect to be long compared to the neutron lifetime, while the ${}^3$He relaxation times may be important for the \emph{nEDM} experiment.

5 Pages, 4 Figures, 1 Table. Submitted to Phys. Rev. A