2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/44209We study the rare decays $B_s^0\to D^\pm π^\mp$ and $\bar B_s^0\to D^\mp π^\pm$, which can occur only via annihilation type $W$ exchange diagrams in the standard model. The time-dependent decay rates of the four channels can provide four CP parameters, which are experimentally measurable. We show that the CKM angle $ϕ_3=γ$ can be determined from these parameters without any theoretical model dependence. These channels can be measured in future LHCb experiments to provide a clean way for $γ$ measurement.4 pages, including 2 figures, RevtexHigh Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext