When a neutron decays, it emits a proton, an electron, and a neutrino in a process known
as beta decay. Measurement of the correlations between these outgoing particles and the
initial polarization of the neutron reveals details of the weak nuclear force, which is one
of the four fundamental forces of nature. The Ultra-Cold Neutron (UCN) A experiment
at LANSCE completed a first measurement of the A correlation parameter, which relates
the outgoing electron’s momentum to the polarization of the decaying neutron. Previous
measurements of this parameter have been plagued by systematic uncertainties and
backgrounds, but have hinted at new physics beyond the standard model of nuclear and
particle physics. The UCNA experiment reduces the uncertainties and backgrounds by
using ultra-cold neutrons to perform the measurement.