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') oscillations as a function of an applied magnetic field B. In the presence of a mirror magnetic field B', ultracold neutron losses would be maximal for B approximate to B'. We did not observe any indication for nn' oscillations and placed a lower limit on the oscillation time of tau(nn') > 12.0 s at 95% C.L. for any B' between 0 and 12.5 mu T.