Observation of a nonzero EDM would imply CP violation beyond the Standard Model. Several years ago, our group established an upper limit of |dHg| < 2.1 × 10-28 ecm for the EDM of 199Hg. To further refine these measurements, we switched from two to four spin-polarized Hg vapor cells: two lie in parallel magnetic and anti-parallel electric fields, resulting in EDM-sensitive spin precession; the remaining two cells, at zero electric field, serve to cancel noise generated by magnetic field gradients and test for systematics due to charging and leakage currents. To prevent experimenter bias from influencing the data, we have also instituted a blind analysis protocol whereby a randomly generated, hidden, and EDM-mimicking frequency shift is applied to the EDM-sensitive frequency channels. We have completed a new data set with the four cell system. The statistical error for the new EDM data is 1.1 × 10-29 ecm, a significant improvement over the 2001 result quoted above. The central value of the new result with the blind offset removed will be presented along with an accounting of the systematic errors of the experiment.
ANL Physics Division Colloquium Schedule