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This content will become publicly available on April 12, 2023

Title: Measurement of the H3∆₁ Radiative Lifetime in ThO
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 H3Δ1 state of thorium monoxide (ThO) molecules, with an observation time τ≈1 ms for each molecule. We report here a new measurement of the lifetime of the ThO (H3Δ1) state, τH=4.2±0.5 ms. Using an apparatus within which τ≈τH will enable a substantial reduction in uncertainty of an eEDM measurement.
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  1. Abstract

    The best upper limit for the electron electric dipole moment was recently set by the ACME collaboration. This experiment measures an electron spin-precession in a cold beam of ThO molecules in their metastableH(3Δ1)state. Improvement in the statistical and systematic uncertainties is possible with more efficient use of molecules from the source and better magnetometry in the experiment, respectively. Here, we report measurements of several relevant properties of the long-livedQ(3Δ2)state of ThO, and show that this state is a very useful resource for both these purposes. TheQstate lifetime is long enough that its decay during the time of flight in the ACME beam experiment is negligible. The large electric dipole moment measured for theQstate, giving rise to a large linear Stark shift, is ideal for an electrostatic lens that increases the fraction of molecules detected downstream. The measured magnetic moment of theQstate is also large enough to be used as a sensitive co-magnetometer in ACME. Finally, we show that theQstate has a large transition dipole moment to theC(1Π1)state, which allows for efficient population transfer between the ground stateXmore »width='0.50em'/>(1Σ+)and theQstate viaXCQStimulated Raman Adiabatic Passage (STIRAP). We demonstrate 90 % STIRAP transfer efficiency. In the course of these measurements, we also determine the magnetic moment ofCstate, theXCtransition dipole moment, and branching ratios of decays from theCstate.

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