Electron electric dipole moment

Quantity relating an electron's potential energy to electric field strength

The electron electric dipole moment de is an intrinsic property of an electron such that the potential energy is linearly related to the strength of the electric field:

The electron's electric dipole moment (EDM) must be collinear with the direction of the electron's magnetic moment (spin). Within the Standard Model of elementary particle physics, such a dipole is predicted to be non zero but very small, at most 10−38 e⋅cm, where e stands for the elementary charge. The discovery of a substantially larger electron electric dipole moment would imply a violation of both parity invariance and time reversal invariance.

In the Standard Model, the electron EDM arises from the CP violating components of the CKM matrix. The moment is very small because the CP violation involves quarks, not electrons directly, so it can only arise by quantum processes where virtual quarks are created, interact with the electron, and then are annihilated. but some other parameter choices or other supersymmetric models lead to smaller predicted values. The present experimental limit therefore eliminates some of these technicolor/supersymmetric theories, but not all. Further improvements, or a positive result, would place further limits on which theory takes precedence.

Electron EDMs are usually not measured on free electrons, but instead on bound, unpaired valence electrons inside atoms and molecules. In these, one can observe the effect of as a slight shift of spectral lines. The sensitivity to scales approximately with the nuclear charge cubed. For this reason, electron EDM searches almost always are conducted on systems involving heavy elements. To date, no experiment has found a non zero electron EDM. As of 2020 the Particle Data Group publishes its value as Here is a list of some electron EDM experiments after 2000 with published results:
+List of Electron EDM ExperimentsYearLocationPrincipal InvestigatorsMethodSpeciesExperimental upper limit on 2002 University of California, Berkeley Eugene Commins, David DeMille Atomic beam Tl 1.6 2011 Imperial College London Edward Hinds, Ben Sauer Molecular beam YbF 1.1 2014 Harvard Yale(ACME I experiment) David DeMille, John Doyle, Gerald Gabrielse Molecular beam ThO 8.7 2017 JILA Eric Cornell, Jun Ye Ion trap HfF+ 1.3 2018 Harvard Yale(ACME II experiment) David DeMille, John Doyle, Gerald Gabrielse Molecular beam ThO 1.1 2022 JILA Eric Cornell, Jun Ye Ion trap HfF+ 4.1

The ACME collaboration is, as of 2020, developing a further version of the ACME experiment series. The latest experiment is called Advanced ACME or ACME III and it aims to improve the limit on electron EDM by one to two orders of magnitude.