PM: Development Towards a Tabletop Experiment with Unprecedented Sensitivity to Hadronic CP Violation

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Our understanding of fundamental physics still leaves many mysteries unsolved, such as the disappearance of antimatter after the big bang (when it was created in equal amounts with matter), and what yet-undiscovered new particles and forces may exist. Certain room-scale experiments are able to explore these questions in ways complementary to studies at large particle accelerators. The research under this grant aims to develop a new approach to such a small experiment, which would search for a tiny deformation in the distribution of electric charge in a nucleus, known as a Schiff Moment, that can only be caused by new particles carrying forces that could explain the cosmological matter-antimatter asymmetry. This new method promises to increase the sensitivity to this deformation by a factor of 1000 beyond the state of the art, and would probe the existence of certain particles hundreds of times heavier than any that could be produced at even the world's largest particle colliders today. Under this grant the group aims to perform two major steps needed to implement this method: create an ultracold gas of silver atoms, and develop a continuous source of francium-223 atoms. The grant will support training of two Ph.D. students in quantum science; it will also enable new initiatives to convey the excitement and accessibility of optical and quantum physics to underprivileged students on Chicago’s South Side. The proposed new measurement will use an optically-trapped, ultracold gas of the polar molecule 223FrAg to search for the Schiff Moment of francium-223. This approach combines many advantageous features at once, relying almost entirely on proven techniques. The 223Fr nucleus is pear-shaped, which enhances its Schiff Moment by a factor of nearly 1000. The FrAg molecule forms a strong polar bond that enhances the measurable signal by another factor of about 10,000. The simple structure of both Fr and Ag atoms has allowed them to be laser-cooled and trapped before. When trapped together, pairs of each atom can be assembled into FrAg molecules without heating, using methods applied to many other, similar atom pairs. The measurement precision relies on a long coherence time of a nuclear spin superposition, which has also been demonstrated in similar molecules under similar conditions. Creating this trapped sample of ultracold 223FrAg molecules will require forming a Bose-Einstein condensate (BEC) of both atoms, which in turn requires measuring the unknown ultracold scattering properties of both atoms. The group will make these measurements for silver atoms, then form the first BEC of silver. Because 223Fr has a short half-life, the group will in parallel develop a high-flux, continuous source of 223Fr atoms that will later be used to perform analogous steps for francium. To achieve the broader impacts in the community, the group will expand the existing SMART program of outreach to local schools, in part by initiating regular “lunch with a scientist” gatherings.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.