  Built on the seminal works by Jackson-Treiman-Wyld and Ebel-Feldman, we
derive the most general free neutron differential decay rate where all massive
particles (neutron, proton and electron) are polarized. This introduces 33 new
correlations in addition to the 18 existing ones, which over-constrain the
coupling constants in the low-energy effective field theory of charged weak
interactions, and thus provides stringent tests of the validity of the theory
framework itself. We classify the correlation coefficients in terms of their
Standard Model limit and discrete symmetries, and study their expansion with
respect to the new physics coupling strengths, supplemented by the
experiment-independent $\mathcal{O}(\alpha)$ virtual electromagnetic radiative
corrections.
