Progress Towards an Order of Magnitude Improvement on the Measurement of the Electron Electric Dipole Moment*

The search for the electron electric dipole moment (eEDM) is a powerful probe of fundamental physics beyond the Standard Model. In 2014, the first generation of the ACME experiment set the most stringent upper limit on the eEDM of $|d_e|<1\times10^{−28}~e \cdot cm$ by means of measuring spin precession in a beam of thorium monoxide (Science 343 (2014), 269-272). Since then, we have implemented various improvements, such as STIRAP preparation of the experimental H state, rotational cooling, optimized apparatus geometry, and enhanced detection efficency, boosting our signal by a factor of about 400. We have also devised means to reduce the leading systematics we found in the Generation I experiment. We describe the recent progress in taking data using our Generation II apparatus and our ongoing efforts to investigate various systematics.