Laboratory constraints on peV-scale mass splitting between ordinary and sterile neutron states

Abstract

Sterile states of matter, represented by a parallel ``mirror'' sector, may contribute to the observed dark matter in the Universe. We investigated the parameter space of neutron $(n)$ to mirror-neutron $(n^{\prime })$ oscillations, in the case where the two states are not necessarily mass-degenerate, taking into account interactions in the mirror sector. By tuning the magnitude of an applied magnetic-field in the range $5\mu \mathrm{T}<B<360\mu \mathrm{T}$ to corresponding resonance conditions for finite mass splitting, we derive exclusion limits for the $n-n^{\prime }$ oscillation time constant reaching about $20\text{s}$ over the mass-difference range $0.3-22\text{peV}$. In parts of this parameter range, our limits exceed the model-dependent neutron-star-cooling bound, providing the first experimental constraints in this scenario that are more stringent than this astrophysical estimate.

7 pages, 4 figures