2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/46258A brief review of checking the factorization hypothesis for matrix element of $B^0 - \bar B^0$ mixing within operator product expansion and QCD sum rules is given. Both perturbative and power corrections are considered.LaTeX file, 7 pagesHigh Energy Physics - Phenomenologytext