AMO Seminar Series - Dr. Kent Leung

Abstract: Fast neutrons from fission or spallation, which are created with MeV energies, can be cooled to < 300 neV to become ultracold neutrons (UCNs). This 12 orders-of-magnitude energy reduction allows them to be trapped in material bottles or magnetic traps and be studied for tens of minutes. High-precision UCN experiments using UCNs have impact in nuclear physics, particle physics, fundamental symmetries, cosmology, and condensed matter physics. A flagship experiment is the search for a permanent neutron electric dipole moment (nEDM). Its detection would be an indication of a new beyond-standard-model source of time-reversal symmetry violation, one that is needed to explain the excess of matter to anti-matter in the Universe from baryogenesis. Since the 1980s the most precise measurements have come from using Ramsey’s
separated oscillatory fields technique on UCNs. Our collaboration will perform a new experiment at the Spallation Neutron Source (SNS) at Oak Ridge National Lab using a novel technique that exploits unique properties of combining polarized UCNs and polarized 3He in a superfluid 4He bath at 0.4 K. Two distinct measurement modes can be performed with our setup: double free precession and critical spin dressing. Our sensitivity goal is a two orders-of-magnitude improvement on the current world limit in both statistics and systematics. This seminar will give a brief overview of UCNs and then focus on the nEDM@SNS experiment, which is envisioned to come online in the next few years. Overlaps with AMO physics will be highlighted where possible.