In polarized neutron decay, the angular correlation between the neutron spin and the
direction of emission of the electron is characterized by the coefficient A. Measuring
A involves determining the forward-backward asymmetry of the decay beta with
respect to the direction of the neutron polarization. The value of A, when combined
with measurements of the neutron lifetime, determines the values of the vector and
axial vector weak coupling constants, Gv and GA. The value of Gv can also be
determined by measurements of superallowed nuclear beta decay and by requiring
that the Cabibo-Kobayashi-Maskawi (CKM) mixing matrix be unitary along with the
measured value of other elements of the CKM matrix
