https://peeterjoot.com/2018/11/13/phy2403h-quantum-field-theory-lecture-16-differential-cross-section-scattering-pair-production-transition-amplitude-decay-rate-s-matrix-connected-and-amputated-diagrams-vacuum-fluctuation-s/
PHY2403H Quantum Field Theory. Lecture 16: Differential cross section, scattering, pair production, transition amplitude, decay rate, S-matrix, connected and amputated diagrams, vacuum fluctuation, symmetry coefficient. Taught by Prof. Erich Poppitz