Measurement of the H${}^3\hat{I}{”}_1$ Radiative Lifetime in ThO

Abstract

The best limit on the electron electric dipole moment (eEDM) comes from the ACME II experiment [Nature \textbf{562} (2018), 355-360] which probes physics beyond the Standard Model at energy scales well above 1 TeV. ACME II measured the eEDM by monitoring electron spin precession in a cold beam of the metastable H${}^3\hat{I}{”}_1$ state of thorium monoxide (ThO) molecules, with an observation time $\ddot{I}„\approx 1$ ms for each molecule. We report here a new measurement of the lifetime of the ThO (H${}^3\hat{I}{”}_1$) state, $\ddot{I}{„}_H=4.2\pm 0.5$ ms. Using an apparatus within which $\ddot{I}„\approx \ddot{I}{„}_H$ will enable a substantial reduction in uncertainty of an eEDM measurement.

6 pages, 5 figures