Models that postulate the existence of hidden sectors address contemporary questions, such as the source of baryogenesis and the nature of dark matter. Neutron-to-hidden-neutron oscillations are among the possible mixing processes and have been tested with ultracold neutron storage and passing-through-wall experiments to set constraints on the oscillation period ${\tau }_{n{n}^{\prime }}$. These searches probe the oscillations as a function of the mass splitting due to the neutron-hidden-neutron energy degeneracy. In this work, we present a new limit derived from neutron disappearance in ultracold neutron beam experiments. The overall limit, given by ${\tau }_{n{n}^{\prime }}>1\mathrm{s}\text{for\hspace{0.17em}}|\delta m|\in [2,69]\mathrm{peV}(95.45\%\mathrm{C}.\mathrm{L}.)$, covers the yet unexplored intermediate mass-splitting range and contributes to the ongoing research on hidden sectors.

• Received 22 March 2023
• Revised 18 September 2023
• Accepted 6 October 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.191801

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society