Experimental search for neutron - mirror neutron oscillations using storage of ultracold neutrons

Understand

The idea of a hidden sector of mirror partners of elementary particles has attracted considerable interest as a possible candidate for dark matter.

• Recently it was pointed out by Berezhiani and Bento that the present experimental data cannot exclude the possibility of a rapid oscillation of the neutron n to a mirror neutron n' with oscillation time much smaller than the neutron lifetime.
• A dedicated search for vacuum transitions n->n' has to be performed at weak magnetic field, where both states are degenerate.
• We report the result of our experiment, which compares rates of ultracold neutrons after storage at a weak magnetic field well below 20 nT and at a magnetic field strong enough to suppress the seeked transitions.