Measurement of the H$^3\Delta_1$ Radiative Lifetime in ThO

TL;DR

This paper reports a new measurement of the H$^3\Delta_1$ state lifetime in ThO molecules, which is crucial for improving the precision of electron EDM experiments that test physics beyond the Standard Model.

Contribution

The paper provides the first precise measurement of the ThO H$^3\Delta_1$ state lifetime, enabling enhanced accuracy in future eEDM experiments.

Findings

Measured lifetime $ au_H = 4.2 \pm 0.5$ ms for ThO H$^3\Delta_1$ state.

The new lifetime measurement can significantly reduce uncertainties in eEDM experiments.

Supports improved constraints on physics beyond the Standard Model.

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$^3\Delta_1$ state of thorium monoxide (ThO) molecules, with an observation time $\tau \approx 1$ ms for each molecule. We report here a new measurement of the lifetime of the ThO (H$^3\Delta_1$) state, $\tau_H = 4.2\pm 0.5$ ms. Using an apparatus within which $\tau \approx \tau_H$ will enable a substantial reduction in uncertainty of an eEDM measurement.