Ready for its close-up: The electron’s permanent electric dipole moment

A new study with direct implications for one of the most important unresolved questions in physics – the imbalance of matter and antimatter in our universe – reports “the most precise measurement yet” of the size of the electron’s permanent electric dipole moment. The imbalance between matter and antimatter in the Universe can be explained via the breaking of charge parity symmetry. The standard model (SM) of particle physics predicts a slight breaking of this symmetry, but it is insufficient to explain the imbalance actually observed. Many extensions to the standard model have been proposed to resolve this discrepancy. To test such model extensions, tabletop experiments that measure the electric dipole moment of the electron (eEDM) – a measure of symmetry breaking – have been very promising. Here, seeking to measure the eEDM with extremely high precision, Tanya Roussy et al. used a powerful approach: electrons confined inside molecular ions, subjected to a huge intramolecular electric field. “Considerable effort by Roussy et al. went into meticulously studying their experimental apparatus and measurement technique so they could understand systematic uncertainties in minute detail to ensure that no spurious signals were mistakenly introduced,” write Mingyu Fan and Andrew Jayich in a related Perspective. Their result improves on the previous best upper bound of the size of the eEDM by a factor of ~2.4.