Improved Limits on n → n' Transformation from the Spallation Neutron Source and Preliminary Results from the High Flux Isotope Reactor*

The known-dominance of matter over antimatter in the observed universe cannot be explained by the Standard Model of Particle physics. The explanation of this imbalance requires the violation of Baryon number Β (the total number of protons and neutrons in nature). Conversions between neutrons n and a Dark Matter mirror neutron n' have been proposed as such a mechanism for this Β violation. In the special case that there is a small mass △m between the n and n' states, oscillations can be enhanced by compensating for the △m with a magnetic field. Utilizing a regeneration (n → n' → n) method, a search for such oscillations was performed at the Spallation Neutron Source by placing a thin cadmium wafer inside a 5 T superconducting magnet. We observed no regenerated neutrons above the background. In our new paper, improved limits for regeneration transformation have been set in terms of the model parameters. As well, a preliminary result of an improved experiment performed at the High Flux Isotope Reactor earlier this year are discussed.