2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/42422I compare collinear and $k_T$ factorization theorems in perturbative QCD, and discuss their application to exclusive $B$ meson decays. Especially, I concentrate on the recently measured time-dependent CP asymmetry of the $B^0_d\toπ^+π^-$ modes, from which the unitarity angle can be extracted.4 pages, talk presented at the XXXVIIIth Rencontres de Moriond session on QCD And High Energy Hadronic Interactions, Les Arcs 1800, France, Mar. 22-29, 2003High Energy Physics - Phenomenologytext