  The possibility of relatively fast neutron oscillations into a mirror neutron
state is not excluded experimentally when a mirror magnetic field is
considered. Direct searches for the disappearance of neutrons into mirror
neutrons in a controlled magnetic field have previously been performed using
ultracold neutrons, with some anomalous results reported. We describe a
technique using cold neutrons to perform a disappearance and regeneration
search, which would allow us to unambiguously identify a possible oscillation
signal. An experiment using the existing General Purpose-Small Angle Neutron
Scattering instrument at the High Flux Isotope Reactor at Oak Ridge National
Laboratory will have the sensitivity to fully explore the parameter space of
prior ultracold neutron searches and confirm or refute previous claims of
observation. This instrument can also conclusively test the validity of
recently suggested oscillation-based explanations for the neutron lifetime
anomaly.
