Neutron lifetime measurements using gravitationally trapped ultracold neutrons

Experiments using gravitationally trapped ultracold neutrons (UCNs) to measure the neutron lifetime are 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, $878.5\pm 0.7_{\text{stat}}\pm 0.3_{\text{sys}}$ s, is the most accurate one to date. The impact of the new result on testing the unitarity of the quark mixing matrix and on data analysis for the primordial nucleosynthesis model is scrutinized.