Measurements of an Electric Dipole Moment using Polarized ³He for the NOPTREX Experiment

To explain the Baryon Asymmetry of the Universe, the predominance of matter over antimatter, a new source of Charge-Parity (CP) violation beyond what is already accounted for in the Standard Model is necessary. By the CPT theorem, which states that the combination of charge conjugation (C), parity transformation (P), and a time reversal (T) will behave exactly like the non-inverted system, direct tests of (T) violation are equivalent to searches for (CP)-violation. A prime candidate for (T)-violation is the electric dipole moment (EDM) of fundamental particles. The EDM of ³He was measured by placing a cell of polarized ³He in a static magnetic field, created by a Helmholtz coil, that is parallel to the spins of the ³He atoms and a static electric field that is either parallel or antiparallel. The nuclear spins of ³He precess in the magnetic field after being tipped in the transverse orientation by a smaller RF Helmholtz coil, driven at the Larmor precession frequency. Small modulations of the actual precession frequency with respect to the direction of a strong electric field are measured with a pickup coil, with this modulation in frequency being sensitive to the EDM. This experiment was performed at the University of Nagoya, with a measured ³He EDM of d = 2.3690 × 10^-16 e · cm. The experiment procedure, statistical and systematic certainties are addressed herein.

*This work was funded in part by the NSF under grant PHY-2246335