Improved limits on 𝑛→𝑛′ transformation from the Spallation Neutron Source

Abstract

Conversions between neutrons 𝑛 and dark matter candidate sterile neutrons 𝑛′ have been proposed as a mechanism for baryon number ℬ violation. In the case that there is a small mass difference Δ⁢𝑚 between the 𝑛 and the 𝑛′ states, oscillations can be induced by compensating for Δ⁢𝑚 with a magnetic field. A search for such neutron oscillations was performed at the Spallation Neutron Source by looking for anomalous neutron transmission through a strongly absorbing cadmium wafer inside of a 6.6 T magnet. The approach described here saw no regenerated neutrons above background, which provides an improved limit for neutron–sterile neutron transformations for a range of Δ⁢𝑚 between 0.1 and 1000 neV.