The Electric Dipole Moment of Radium

The apparent excess of matter over anti-matter throughout the universe is one of the most pressing challenges in all of physics. This is because nature appears to respect the symmetry known as CP (charge conjugation-parity) almost perfectly, which implies matter and anti-matter should have been produced with precisely the same abundance during the Big Bang. Thus, new undiscovered sources of CP-violation are needed to explain the baryon asymmetry of the universe, and these sources feature prominantly in new theories that extend the standard model of particle physics, such as supersymmetry. Electric dipole moments (EDMs) are signatures of time-reversal, parity, and charge parity (CP) violation, which make them a sensitive probe of such physics. Due to its large nuclear octupole deformation and high atomic mass, the radioactive Ra-225 isotope is a favorable EDM case; it is particularly sensitive to CP-violating interactions in the nuclear medium. To measure this rare isotope, we have developed an approach to measuring EDMs by using lasers to cool those atoms to 40 micro-Kelvins, and trapping them in a optical dipole trap. Using this method, we have found the EDM of radium to be less than 1.4e-23 e-cm (95% C.L). Recent improvements to the apparatus that will dramatically improve its sensitivity in the near term will be discussed.