Grant: Subatomic Physics Envelope - Project

The excess of matter over antimatter in the universe is one of the biggest puzzles of our time. Solutions to this puzzle require that fundamental time-reversal symmetry be violated to a much larger extent than is possible within the existing Standard Model of physics, suggesting that undiscovered new physics could be responsible for such a basic property of our universe. A powerful way to discover hints of new physics is to search with ultrahigh precision for a permanent electric dipole moment of fundamental particles such as electrons. We are continuing to build an electron electric dipole moment (eEDM) search experiment that may improve upon the current best measurements by up to five orders of magnitude. Modern eEDM measurements take advantage of the large effective electric field seen by an unpaired electron in a heavy polar molecule. To make a large leap in precision, a radical new technique is required. Our method uses a large ensemble of barium monofluoride (BaF) molecules trapped in a cryogenic argon (Ar) solid to perform an eEDM search. The Ar crystal lattice fixes the orientation and position of the BaF molecules, allowing for BaF molecules produced over several hours to be accumulated into an Ar solid during deposition of Ar gas onto a cryogenically cooled sapphire substrate. In addition to greatly increasing the number of molecules addressable, trapping BaF molecules in this way also improves the measurement time, further improving the potential precision of the measurement. The fact that the molecules are not in motion in the solid, are oriented by the solid (and therefore do not require an external electric field), and are contained in a small volume (<1 mm3) serves to eliminate many classes of potential systematic effects. The system  is naturally equipped with excellent comagnetometers (using simultaneous measurements on interspersed oppositely-oriented molecules) to suppress errors from magnetic field fluctuations, allowing it to be used in an advanced eEDM experiment. All of these features together should enable an eEDM measurement with new physics sensitivity out to peta-electron-volt energy scales. The proposed research is being undertaken by the EDM3 Collaboration (University of Toronto, York University, and Michigan State University) using an apparatus located at York. A recent Canada Foundation for Innovation award (with matching funds from the Ontario Research Fund) has provided 6.72 million dollars for equipment and infrastructure for the work. Precision eEDM measurements are a model-independent and vitally important complement to collider experiments for discovering new physics. This is the first Canadian effort of its kind and we aim to achieve a level of sensitivity to new physics that is many orders of magnitude beyond any other current or proposed experiment. This experiment will place the Canadian subatomic physics community in a world-leading position at the precision frontier of high-energy physics.