The imbalance of matter and antimatter in our Universe provides compelling motivation to search for undiscovered particles that violate charge-parity symmetry. Interactions with vacuum fluctuations of the fields associated with these new particles will induce an electric dipole moment of the electron (eEDM). We present the most precise measurement yet of the eEDM using electrons confined inside molecular ions, subjected to a huge intramolecular electric field, and evolving coherently for up to 3 seconds. Our result is consistent with zero and improves on the previous best upper bound by a factor of ~2.4. Our results provide constraints on broad classes of new physics above
Improved limit on the electric dipole moment of the electron
The standard model of particle physics accurately describes all particle physics measurements made so far in the laboratory. However, it is unable to answer many questions that arise from cosmological observations, such as the nature of dark matter and why matter dominates over antimatter throughout the Universe. Theories that contain particles and interactions beyond the standard model, such as models that incorporate supersymmetry, may explain these phenomena. Such particles appear in the vacuum and interact with common particles to modify their properties. For example, the existence of very massive particles whose interactions violate time-reversal symmetry, which could explain the cosmological matter–antimatter asymmetry, can give rise to an electric dipole moment along the spin axis of the electron. No electric dipole moments of fundamental particles have been observed. However, dipole moments only slightly smaller than the current experimental bounds have been predicted to arise from particles more massive than any known to exist. Here we present an improved experimental limit on the electric dipole moment of the electron, obtained by measuring the electron spin precession in a superposition of quantum states of electrons subjected to a huge intramolecular electric field. The sensitivity of our measurement is more than one order of magnitude better than any previous measurement. This result implies that a broad class of conjectured particles, if they exist and time-reversal symmetry is maximally violated, have masses that greatly exceed what can be measured directly at the Large Hadron Collider.
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- Award ID(s):
- 1734011
- NSF-PAR ID:
- 10094514
- Date Published:
- Journal Name:
- Nature
- Volume:
- 562
- Issue:
- 7727
- ISSN:
- 0028-0836
- Page Range / eLocation ID:
- 355 to 360
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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electron volts, beyond the direct reach of the current particle colliders or those likely to be available in the coming decades. -
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.more » « less
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Ultracold polyatomic molecules are promising candidates for experiments in quantum science and precision searches for physics beyond the Standard Model. A key requirement is the ability to achieve full quantum control over the internal structure of the molecules. In this work, we established coherent control of individual quantum states in calcium monohydroxide (CaOH) and demonstrated a method for searching for the electron electric dipole moment (eEDM). Optically trapped, ultracold CaOH molecules were prepared in a single quantum state, polarized in an electric field, and coherently transferred into an eEDM-sensitive state where an electron spin precession measurement was performed. To extend the coherence time, we used eEDM-sensitive states with tunable, near-zero magnetic field sensitivity. Our results establish a path for eEDM searches with trapped polyatomic molecules.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41586-018-0599-8
