A New Lifetime Measurement of the H³Δ₁ state of Thorium Monoxide for the ACME electron EDM experiment

The electron electric dipole moment (EDM) is a powerful probe for new physics beyond the Standard Model. The ACME experiment measures the electron EDM by performing spin precession in the H$^3\Delta_1$ state of thorium monoxide. In 2018, the ACME II experiment set the most stringent upper limit on the electron EDM: $|d_e|<1.1\times10^{-29}\ \textup{e}\cdot \textup{cm}$ (\textit{Nature}, \textbf{562}(2018) 355-360). The next generation of the experiment is currently under development. We have recently performed a measurement of the lifetime of the H-state in a molecular beam, finding it to be $\sim$4.5 times longer than the precession time in the ACME II experiment. This allows us to increase the precession time in ACME III, significantly improving its statistical sensitivity to the electron EDM. Together with other improvements under development, this provides a path towards an order of magnitude statistical improvement in probing the electron EDM.