Improved limit on the electric dipole moment of the electron.

Abstract

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 thatcontain particles and interactions beyond the standard model, such as models thatincorporate supersymmetry, may explain these phenomena. Such particles appearin the vacuum and interact withcommon particles to modify their properties. For example, the existence of very massive particles whose interactions violate time-reversal symmetry, which couldexplain 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 momentof 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 thanone 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 bemeasured directlyat the Large Hadron Collider.