Neutron optical studies on ultracold neutron anomaly in bottled neutron experiments

Ultracold neutrons (UCN) with the energy below the potential barrier for total reflection of a mirror can be confined for a long time of several hundreds seconds in a closed vessel with the inner surfaces made of the neutron mirror. However, the experimental storage lifetime of UCN reported on bottles with clean and low absorption surface remains significant discrepancy with the theoretical one. Present paper reports on our recent studies concerning two kinds of possible causes supposed of the UCN anomaly, i.e. one is the possibility of UCN micro-heating during the storage and the other is the possible effects of sub-barrier transmission in the de Broglie wave-packet hypothesis of the neutron, and the results indicating the subcritical transmission probability obtained on a silicon mirror in consistent with the UCN loss probability from the bottle experiment with assuming a constant packet width of the neutron. (author)