Search for neutron - mirror neutron oscillations in a laboratory   experiment with ultracold neutrons
  Mirror matter is considered as a candidate for dark matter. In connection with this an experimental search for neutron - mirror neutron (nn') transitions has been carried out using storage of ultracold neutrons in a trap with different magnetic fields. As a result, a new limit for the neutron - mirror neutron oscillation time has been obtained, tau_osc >= 448 s (90% C.L.), assuming that there is no mirror magnetic field larger than 100 nT. Besides a first attempt to obtain some restriction for mirror magnetic field has been done. 
A. P. Serebrov, E. B. Aleksandrov, N. A. Dovator, S. P. Dmitriev, A.   K. Fomin, P. Geltenbort, A. G. Kharitonov, I. A. Kras...