Neutron to mirror-neutron oscillations in the presence of mirror magnetic fields

We performed ultracold neutron storage measurements to search for additional losses due to neutron ($n$) to mirror-neutron (${n}^{\ensuremath{'}}$) oscillations as a function of an applied magnetic field $B$. In the presence of a mirror magnetic field ${B}^{\ensuremath{'}}$, ultracold neutron losses would be maximal for $B\ensuremath{\approx}{B}^{\ensuremath{'}}$. We did not observe any indication for $n{n}^{\ensuremath{'}}$ oscillations and placed a lower limit on the oscillation time of ${\ensuremath{\tau}}_{n{n}^{\ensuremath{'}}}>12.0\text{ }\text{ }\mathrm{s}$ at 95% C.L. for any ${B}^{\ensuremath{'}}$ between 0 and $12.5\text{ }\text{ }\ensuremath{\mu}\mathrm{T}$.