2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/214530Most of this paper consists of the derivation of general beam-referenced stage-two spin-correlation functions for the analysis of top-antitop pair-production at the Tevatron, at the Large Hadron Collider, and/or at an International Linear Collider. However, for the charged-lepton-plus-jets reaction $q \bar{q} \to t \bar{t} \to (W^+ b) (W^- \bar{b}) \to (l^{+} νb) (W^- \bar{b})$, there is a simple 3-angle spin-correlation function for determination of the relative sign of, or for measurement of a possible non-trivial phase between the two dominant $λ_b = -1/2 $ helicity amplitudes for the $t\to W^{+}b$ decay mode. For the CP-conjugate case, there is an analogous function and tests for $\bar{t} \to W^{-} \bar{b}$ decay. These results make use of W-boson longitudinal-transverse interference.Version 4 as to appear in EPJC. Minor editing includes resequencing and renumbering eqs. 117-120High Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext