Physical Review C Editor's suggestion: The imbalance between matter and antimatter in our Universe remains one of the great mysteries of modern physics. The neutron’s electric dipole moment (EDM) is a sensitive probe of new sources of CP violation that could help explain this asymmetry. Searches for an EDM rely on extraordinarily precise measurements of the neutron spin precession, using polarized mercury atoms to monitor the applied magnetic field. But the mercury atoms themselves can interact with neutrons in a way that produces a tiny, spin-dependent frequency shift, potentially mimicking an EDM signal. In this study, the nEDM Collaboration, with the experiment based at the Paul Scherrer Institute, directly investigates this subtle neutron-mercury interaction. The results provide a precise characterization of an important systematic effect, improving the control of a key source of uncertainty in EDM measurements.
