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Physics Colloquium: "Search for the Electric Dipole Moment of the Electron with ThO – 10 TeV physics on the 'table top'"

Event Type
Department of Physics
141 Loomis
Apr 26, 2017   4:00 pm  
John Doyle, Harvard University
Stephanie Johansson
Originating Calendar
Physics - Colloquium

In 2014, the ACME collaboration made the most precise measurement of an electric dipole moment (EDM) ever [1,2], constraining the electron's EDM to be de ≤ 9.3 x 10-29

At the same time, the Large Hadron Collider was setting records for ever-higher collision energies and luminosities. These two experiments continue to probe for new physics at similar, unprecedented levels of sensitivity – however ACME does so in a university laboratory environment.

The Standard Model of physics is accepted to be incomplete, with no framework to explain fundamental observations such as dark matter and the matter-antimatter asymmetry. Many new theories aim to solve these problems, and the hierarchy problem, by introducing new particles and new sources of CP-violation. The same theories often predict values for the electron EDM (an intrinsically CP-violating observable) significantly higher than expected within the Standard Model. Our measurement of the electron EDM, together with results from the LHC and elsewhere, has severely constrained the viable parameter space for theories of new physics, such as supersymmetry.


Under the typical assumption of order unity phases we are able to place constraints on the mass of the stop (supersymmetric top) particle in the ~TeV range. We also strongly constrain viable parameter space in the chargino sector at the TeV level – here in particular, the electron EDM presents a `uniquely powerful window' onto supersymmetry [3], probing regions of parameter space that are difficult for the LHC to access.

The ACME experiment harnesses the technology of cryogenic buffer gas beams to produce a high-flux source of thorium monoxide (ThO) [4] which, together with the enormous (~GV/cm) effective internal electric field of ThO, enables an unprecedented level of precision. Additionally, the Ω-doublet structure of ThO provides robust rejection of systematic effects within our experiment.

The ACME experiment is currently preparing for our second measurement. We have made several apparatus upgrades that together have increased the usable molecule flux by more than a factor of 100, and we have made a number of improvements to further suppress known systematic effects. Thus, we anticipate that ACME II will soon explore making an electron EDM measurement with an order of magnitude greater statistical sensitivity, potentially increasing the energy reach of EDM searches to the 10 TeV range.


[1] ACME Collaboration, Science 343, 269-272 (2014)

[2] ACME Collaboration, arXiv 1612.09318 (2016)

[3] Nakai and Reece, arXiv 1612.08090 (2016)

[4] Hutzler et al., Phys. Chem. Chem. Phys. 13, 18976-19898 (2011)

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