MRI Consortium: Development of A Room-Temperature Apparatus to Measure the Electric Dipole Moment of the Neutron, for a Fast-Track Ten-Fold Improvement in Sensitivity

Overview: We propose to develop instrumentation needed to improve the sensitivity to the neutron electric dipole moment (nEDM) by a factor of ten, taking advantage of an increased ultracold neutron (UCN) yield from an upgraded UCN source at the Los Alamos National Laboratory (LANL). Achieving this sensitivity requires high densities of polarized UCN and build an apparatus capable of controlling systematic effects. The recently-upgraded UCN source at LANL will provide neutrons for this experiment. The experiment design is based on a two-cell measurement chamber, state-of-the-art room-temperature magnetic shielding, novel magnetic field configurations, and sensitive magnetometry (both external and co-habitating) to control systematics. The proposed activities represent refinements to Ramsey's technique of separated oscillatory fields; this essentially conservative design will allow the instrument to be assembled, tested, and commissioned on the proposed (aggressive) timescale. An order-of-magnitude increase in the LANL UCN source intensity, together with the latest advances in magnetic field controls, will make possible an nEDM search at the 3 10..27 e-cm level of sensitivity. Intellectual Merit: A non-zero nEDM would violate both P and T symmetries; the existing experimental upper limit has strongly influenced intellectual developments in particle physics, astrophysics, and cosmology. The present structure of the Standard Model of elementary particles suggests that symmetries carried by fundamental interactions may be absorbed and unified in a more general symmetry. The neutron is the simplest neutral hadronic system which lives long enough on which to conduct these symmetry tests. A successful nEDM experiment with 3 10..27 e-cm sensitivity will provide the most cleanly-interpretable information on P and T violation in the light quark sector. One of the leading dark matter candidates (axions) was originally proposed to help explain the mysterious absence of T violation in QCD, and the present upper bound on the EDM strongly constrains theories beyond the Standard Model. If no nEDM is discovered, this experiment, in combination with ongoing EDM searches in atomic systems, will push the limits on the mass scale for new T violation physics above 100 TeV with direct sensitivity to the Higgs sector, conclusively test the minimal supersymmetric model for electroweak baryogenesis, and tightly constrain modelindependent analyses of P and T violation. Discovery of a nonzero EDM at this level would reveal a completely new source of T (and thus CP) violation. Broader Impacts: The room-temperature LANL nEDM experiment is a timely scientific opportunity both within a global scientific context and in relation to the ongoing major US effort to mount the cryogenic nEDM experiment at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory. The latter experiment aims for 3x10-28 e-cm in sensitivity. However, that is in the longer-term future. The nEDM search is arguably so important for both its science reach and broader impact that there should be more than one such experiment in the US. Based on our analysis of the present landscape The latter experiment aims for 3 worldwide, if started now, the experiment proposed for LANL will be fully competitive. Furthermore, the technical overlap between the requirements for the LANL and SNS nEDM experiments in the areas of electric field generation, spin manipulation, and especially magnetic field control{an absolutely essential aspect of any successful EDM experiment{is substantial. The proposed activity will develop the knowledge and technical basis to further suppress the systematic errors associated with present experimental approaches. Most importantly, it will contribute to the human resources needed to realize the SNS nEDM experiment. Students will participate in measurements and analysis as part of thesis projects. Lessons learned in the refinement of the instrumentation will inform future experiments. In addition, the generation of dense UCN will lead to prototypes of next-generation neutron sources, since the increase in UCN phase space density will require high-flux cold sources. This in turn will positively affect future applications of neutrons to material and life sciences.