2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/206418The weak phase γcan be determined using untagged B^0\to DK_S or B_s\to Dϕ, Dη^{(')} decays. In the past, the small lifetime difference y\equiv ΔΓ/(2Γ) has been neglected in B^0, while the CP violating parameter ε\equiv 1-|q/p|^2 has been neglected in both B^0-\bar B^0 and B_s-\bar B_s mixing. We estimate the effect of neglecting y and ε. We find that in D decays to flavor states this introduces a systematic error, which is enhanced by a large ratio of Cabibbo-allowed to doubly Cabibbo-suppressed D decay amplitudes.one reference added, to be submitted for publication in Physics Letters BHigh Energy Physics - Phenomenologytext