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 β-decay. The neutron lifetime obtained, 878.5 0.7 0.3 stat sys ± ± s, is the most accurate one to date *) In connection with increasing the interest to details of our experiment we are publishing here the extended version of our first PNPI preprint #2564 (2004) prepared before short publication in Phys. Lett. B 605 (2005) 72-78. † A.P. Serebrov, Petersburg Nuclear Physics Institute, Russian Academy of Sciences, 188300 Gatchina, Leningrad Region, Russian Federation Tel. (7-81371) 46 001 E-mail: [email protected]