Progress towards an improved measurement of the electric dipole moment of the electron

Abstract

The Standard Model (SM) of particle physics is one of the most successful scientific theories, but is unable to explain fundamental features of the universe such as baryon asymmetry. The electron electric dipole moment (eEDM) is a powerful probe of physics beyond the SM. The ACME experiment seeks to measure the eEDM by performing spin precession on a beam of thorium monoxide molecules. In 2018, the ACME II experiment set an upper limit on the eEDM of $|\de| 1.1\times10^{-29}~e\cdot\mathrm{cm}$, which has stood as the most stringent published limit for the last five years. Since then, the next generation ACME III experiment has been developed with the goal of improving upon this measurement by another order of magnitude. Three major sensitivity upgrades (increased spin precession time, an electrostatic molecular lens, and improved photon detection) have been demonstrated, and all known sources of systematic uncertainty will be reduced to well below the projected statistical sensitivity. This work describes the ACME II measurement, the ACME III apparatus, a lifetime measurement of the EDM-sensitive H-state which allows an increase in spin precession time, upgrades to the photon detection and data acquisition systems, and improved control of magnetic fields in the experiment. With these advances, ACME III is well-poised to accomplish its goal of probing new physics at the scales of tens of TeV, comparable to the reach of the Large Hadron Collider.