Improved Limits on $n\to n^{\prime }$ Transformation from the Spallation Neutron Source

Abstract

Conversions between neutrons $n$ and Dark Matter candidate sterile neutrons $n^{\prime }$ have been proposed as a mechanism for Baryon Number $\mathcal{B}$ violation. In the case that there is a small mass difference $\hat{I}”m$ between the $n$ and the $n^{\prime }$ states, oscillations can be induced by compensating for $\hat{I}”m$ 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 neutrons transformations for a range of $\hat{I}”m$ between $0.1$~neV and $1000$~neV.

18 pages, 15 figures