Neutron-Mirror Neutron Oscillations in Absorbing Matter

The possibility that a neutron can be transformed to a hidden sector particle remains intriguingly open. Proposed theoretical models conjecture that the hidden sector can be represented by a mirror sector, and the neutron n can oscillate into its sterile mirror twin n′, exactly or nearly degenerate in mass with n. Oscillations n − n′ can take place in vacuum or in an environment containing regular matter and a magnetic field, in which only the neutron will be subject to interactions with the environment. We describe the propagation of the oscillating n − n′ system in a cold neutron beam passing through dense absorbing materials in connection to the possible regeneration type of experiments, where the effect of n → n′ → n transformation can be observed.