No 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, τ osc (90% C.L.) > 414 s.The corresponding limit for the mixing energy of the normal and mirror neutron states is δm (90% C.L.) < 1.5×10 -18 eV.

Our experiment using gravitationally trapped ultracold neutrons (UCN) to measure the neutron lifetime is reviewed. Ultracold neutrons were trapped in a material bottle covered with perfluoropolyether. The neutron lifetime was deduced from comparison of UCN losses in the traps with different surface-to-volume ratios. The precise value of the neutron lifetime is of fundamental importance to particle physics and cosmology. In this experiment, the UCN storage time is brought closer to the neutron lifetime than in any experiments before: the probability of UCN losses from the trap was only 1% of that for neutron β decay. The neutron lifetime obtained, 878.5 ± 0.7 stat ± 0.3 sys s, is the most accurate experimental measurement to date.A. P. SEREBROV et al. PHYSICAL REVIEW C 78, 035505 (2008) 035505-3 A. P. SEREBROV et al. PHYSICAL REVIEW C 78, 035505 (2008)