Session B2: Frontiers in Precision Measurements-Electric Dipole Moments

ACME Measurement of the Electron Electric Dipole Moment

The standard model of particle physics (SM) is the great triumph and the great frustration of modern physics. The SM is able to correctly predict the measured size of the electron's magnetic dipole moment to a remarkable 12 significant figures. At the same time, the SM predicts that essentially equal amounts of matter and antimatter should have been created in the big bang, and no explanation comes close to predicting the amount of matter that avoided being annihilated in collisions with the antimatter to form a matter universe. The electric dipole moment of the electron provides a unique opportunity to precisely test the standard model, its fundamental symmetries and many proposed modifications. The SM predicts that the electron has an electric dipole moment (EDM), but that this moment should be much too small to be observed with current methods. In distinct contrast, supersymmetric and other models (proposed as improvements to the standard model) predict that the electron could well have an EDM that is much, much larger. These disparate predictions prompted our ACME collaboration to measure the electron electric dipole moment more than an order of magnitude more precisely than ever before. Despite the greatly increased sensitivity of this ACME generation 1 measurement, a non-zero EDM was not detected. Our order of magnitude lower limit has instead been used in many papers to set many limits -- on the masses of postulated new particles, for example. It is worth noting that a measurement done with cold molecules is setting limits whose TeV energy reach is as high and higher than is possible at the largest particle accelerator -- CERN's Large Hadron Collider. New ACME apparatus and methods have recently been demonstrated that we expect to increase our EDM sensitivity by more than an additional order of magnitude. An ACME generation 2 measurement is now underway. An overview of the new methods and aspirations will be provided.   

Search for an Electric Dipole Moment (EDM) of $^{\mathrm{199}}$Hg

The observation of a non-zero EDM of an atom or elementary particle, at current levels of experimental sensitivity, would imply CP violation beyond the CKM matrix of the standard model of particle physics. Additional sources of CP violation have been proposed to help explain the excess of matter over anti-matter in our universe and the magnitude of $\Theta_{QCD}$, the strength of CP violation in the strong interaction, remains unknown. We have recently completed a set of measurements on the EDM of $^{\mathrm{199}}$Hg, sensitive to both new sources of CP violation and $\Theta _{\mathrm{QCD}}$. The experiment compares the phase accumulated by precessing Hg spins in vapor cells with electric fields parallel and anti-parallel to a common magnetic field. Our new result represents a factor of 5 improvement over previous results. A description of the EDM experiment, data, systematic error considerations will be presented.   

Towards a new generation of EDM experiments using molecules

Theories of particle physics that extend the Standard Model frequently predict new phenomena at the TeV scale. These phenomena give rise to electric dipole moments (EDMs) of fundamental particles such as the electron and proton that are within a few orders of magnitude of current limits. The observable effects of EDMs can be enhanced by 3 or more orders of magnitude by using molecules rather than atoms. This talk will describe recent advances in technology for cooling, manipulating, detecting, and trapping molecules that are opening the prospects for significant improvements in sensitivity to EDM-related effects. As an example, the CeNTREX experiment---a new search for the proton EDM and related effects---will be described.   

Electric Dipole Moments: A Look Beyond the Standard Model

Searches for the permanent electric dipole moments of atoms, nucleons, and nuclei provide one of the most powerful probes of CP-violation beyond the Standard Model. I survey the opportunities for discovering BSM CP-violation with the present and next generation EDM searches; discuss the complementary of searches using different systems; and highlight the implications of these searches for explaining the origin of the cosmic matter-antimatter asymmetry.