Neutron lifetime is one of the most important physical constants which
determines parameters of the weak interaction and predictions of primordial
nucleosynthesis theory. There remains the unsolved problem of a 3.9{\sigma}
discrepancy between measurements of this lifetime using neutrons in beams and
those with stored neutrons (UCN). In our experiment we measure the lifetime of
neutrons trapped by Earth's gravity in an open-topped vessel. Two
configurations of the trap geometry are used to change the mean frequency of
UCN collisions with the surfaces - this is achieved by plunging an additional
surface into the trap without breaking the vacuum. The trap walls are coated
with a hydrogen-less fluorine-containing polymer to reduce losses of UCN. The
stability of this coating to multiple thermal cycles between 80 K and 300 K was
tested. At 80 K, the probability of UCN loss due to collisions with the trap
walls is just 1.5% of the probability of beta-decay. The free neutron lifetime
is determined by extrapolation to an infinitely large trap with zero collision
frequency. The result of these measurements is 881.5 +/- 0.7_stat +/- 0.6_syst
s which is consistent with the conventional value of 880.2 +/- 1.0 s presented
by the Particle Data Group. Future prospects for this experiment are in further
cooling to 10 K which will lead to an improved accuracy of measurement. In
conclusion we present an analysis of currently-available data on various
measurements of the neutron lifetime.Comment: 14 pages, 22 figure
