Neutron lifetime measurements using gravitationally trapped ultracold neutrons

Experiment using gravitationally trapped ultracold neutrons (UCNs) to measure the neutron lifetime is reviewed. The precise value of the neutron lifetime is of fundamental importance to particle physics and cosmology. In our experiment, the UCN storage time is brought closest ever to the neutron lifetime: the probability of the UCN loss from the trap was only 1% of that for neutron beta-decay. The neutron lifetime obtained, 878.5+/-0.7stat+/-0.3sys s, is the most accurate one to date