The neutron lifetime: a haiku


Precise knowledge of the free neutron lifetime is required for the prediction of
primordial light element abundances, and is a probe of the charged-current weak
interaction at low energies. The lifetime is primarily measured by either counting
the decay products in a neutron beam of absolutely-known flux, or by trapping
ultracold neutrons (UCN) in material bottles and counting the survivors after
varying time intervals. There is currently a 3.9 standard deviation discrepancy
between these two methods, and new techniques are needed to address this
discrepancy and resolve the neutron lifetime with high precision. The UCNtau
experiment at the Los Alamos Neutron Science Center (LANSCE) consists of a
magnetic UCN trap to eliminate systematic effects related to the absorption and
scattering of neutrons from the walls of previously-used material traps. In addition,
we have developed a novel UCN detector to count the UCN in situ, providing a
powerful check of potential systematic effects. Using the UCNtau apparatus, we
have measured the neutron lifetime to be 877.7 ± 0.7 (stat) +0.3/-0.1 (sys)
seconds, with systematic corrections smaller than their associated uncertainties.
In this talk, I will provide the motivation and context for the measurement, describe
the novel characteristics of the UCNtau experiment, present the results of the
blinded analysis, and discuss potential improvements to the apparatus.

Speaker : 

Daniel Salvat, Ph.D.


CENPA Conference Room NPL-178