Disagreement between measurements of the neutron lifetime by the ultracold neutron storage method and the beam technique

Abstract

Recent measurements of the neutron lifetime performed using a gravitational trap of ultracold neutrons (UCNs) (Konstantinov Petersburg Nuclear Physics Institute, Russia) and a magnetic UCN trap (LANL, USA) have confirmed PNPI’s result of 2005. The results of experiments with stored UCNs agree with each other but differ from those of the beam experiment (NIST, USA) by 3.5σ (corresponding to 1% in the decay probability). This disagreement is currently being discussed in the literature as a ‘neutron anomaly’. We analyze possible reasons for that disagreement and test the experimental data for the neutron lifetime and beta-decay asymmetry within the Standard Model. The test is only passed for neutron lifetime values that are obtained using the UCN storage method.