Progress in the ACME III Search for the Electron EDM

The ACME experiment probes physics beyond the Standard Model by measuring the electron electric dipole moment (eEDM) through a spin precession experiment in a beam of thorium monoxide. In 2018, the second generation of the ACME experiment placed the current upper limit on the eEDM at |d_e|<1.1×10^-29 e·cm (Nature 562(2018), 355-360). The third generation of the experiment is currently under construction. We provide an overview of the experiment and describe upgrades that either have been demonstrated or are under development, such as a longer spin precession time, an electrostatic molecular lens, enhanced fluorescence detection, and improved electric and magnetic field control. Together, the upgrades are projected to increase the statistical sensitivity of the experiment to the electron EDM by an order of magnitude while sufficiently suppressing known sources of systematic error.