2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/124717The measurement of $\sin {2β}$ from $B_d \to J/ψK_s$ does not resolve the discrete ambiguities in the angle $β$. A measurement of $\cos {2β}$ is therefore desirable.This talk is about measuring the CKM angle $β(ϕ_1)$ from various B decays to charm final states which also allow us a measurement of $\cos {2β}$.4 pages, 4 figures. Added references. Talk presented at CKM2006 Workshop, Nagoya, JapanHigh Energy Physics - Phenomenologytext