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

TL;DR

This experiment searches for neutron to mirror neutron oscillations using ultracold neutron storage, setting new limits on oscillation time and mixing energy, which has implications for dark matter models.

Contribution

The paper presents the first dedicated experimental search for n to n' oscillations at weak magnetic fields, establishing new constraints on oscillation parameters.

Findings

Oscillation time tau_osc > 414 seconds at 90% confidence level.

Mixing energy delta_m < 1.5x10^-18 eV at 90% confidence level.

No evidence of neutron to mirror neutron oscillations was observed.

Abstract

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. We obtain a new limit for the oscillation time of n-n' transitions, tau_osc (90% C.L.) > 414 s. The corresponding limit for the mixing energy of the normal and mirror neutron states is delta_m (90% C.L.) < 1.5x10-18 eV.