The electron’s electric dipole moment

The standard model of particle theory predicts a nonzero electric dipole moment (EDM) for the electron. But it’s far too small to detect with present techniques. However, the leading theoretical proposals for new physics beyond the manifestly incomplete standard model predict much larger electron EDMs that would verge on what’s measurable today. Now a team at Imperial College London has used an innovative molecular-beam technique to determine the tightest upper limit yet on the electron’s EDM. Exploiting the enormous electric field felt by the lone unpaired electron inside a polarized ytterbium fluoride molecule, the team has determined, with 90% confidence, that the EDM’s magnitude does not exceed 1.05 × 10^-28 e cm, where e is the quantum of charge. The new null result casts doubt on the simplest version of the popular supersymmetric models proposed for new physics. Actually finding a nonzero electric EDM would help resolve a profound issue in cosmology. A measurable EDM would manifest a new violation of CP symmetry (invariance under the joint operation of particle–antiparticle exchange and mirror inversion) beyond the purview of the standard model, whose only CP-violating mechanism is much too weak to account for the cosmic predominance of matter over antimatter. (J. J. Hudson et al., Nature 473, 493, 2011.)—Bertram Schwarzschild