Order of Magnitude Improved Limit on the Electric Dipole Moment of the Electron

Abstract

The Standard Model of particle physics accurately describes with amazing precision all particle physics measurements made in the laboratory. However, it is unable to answer many central questions that arise from cosmological observations, such as the nature of dark matter and why matter dominates over antimatter throughout the Universe. Theories containing particles and interactions beyond the standard model, such as models incorporating supersymmetry, may explain these phenomena. Such particles can come into virtual existence in the vacuum and then interact with real particles to modify their properties. For example, the existence of very massive particles whose interactions violate time-reversal symmetry, as needed to explain the cosmological matter–antimatter asymmetry, gives rise to an electric dipole moment along the spin axis of the electron. To date no electric dipole moments (EDM), of the electron or other fundamental particles, have been observed. However, dipole moments only slightly smaller than current bounds can arise from new particles more massive than any known to exist. Here we present a new measurement of the electron's electric dipole moment (eEDM), $d_e$=\result, obtained by measuring the spin precession of electrons subjected to the huge intramolecular electric field accessible in the thorium monoxide molecule. The sensitivity of our measurement is one order of magnitude better than any previous work and probes for the existence of new particles with mass far beyond the direct reach of the Large Hadron Collider. Since our measurement is consistent with zero, we report an upper limit of $|d_e|$<\upperlimitFeldman, which sets very strong constraints on a wide range of theories that predict new physics at energy scales directly accessible to colliders.