is an experiment that will probe neutron decay with
unprecedented precision. Previous experiments measuring the correlation
between a neutron's spin and its decay electron's momentum
have arrived at inconsistent results. The UCN-A experiment will measure this
correlation with a factor of four improvement in precision and will
bring our understanding of the weak interaction responsible for
neutron decay to a new level. The results may offer
a glimpse into new phenomena beyond the Standard Model of
The experiment is part of a broader program to develop a high intensity
source of Ultra-Cold Neutrons (UCN) in the United States; a first generation
source is now under construction at Los Alamos National Laboratory. The
source and the experiment began full commissioning in 2005. We expect
to take data for an asymmetry measurement in 2007.
This web page is a resource for the involvement of Caltech
in this project.
We are also involved in another UCN
experiment searching for an electric dipole moment of the neutron.