Neutron lifetime puzzle and neutron–mirror neutron oscillation

Abstract

Standard Model, with its present precision, predicts the neutron β-decay time τSM= 878.7 ± 0.6 s which is perfectly compatible with the neutron lifetime measured in the trap experiments τtrap= 879.4 ± 0.6 s. However, the lifetime measured in the beam experiments via counting the protons produced by β-decay n→ peν¯ e, τbeam= 888 ± 2.0 s, is deviated from τSM by 9 seconds (4.4 σ). This discrepancy can be explained via the neutron n conversion into mirror neutron n′, its dark partner from parallel mirror sector. Provided that n and n′ have a tiny mass splitting ∼ 10 - 7 eV, in magnetic fields of few Tesla used in beam experiments, n- n′ transition is resonantly enhanced converting a 1% fraction of neutrons into mirror neutrons which decay in invisible mode n′→p′e′ν¯e′. Thus less protons are produced and the measured value τbeam appears larger than the true decay time τSM= τtrap.