It is expected that, within the next three years, the determination of the CKM matrix elements with the least theoretical uncertainty will arise from the measurements of $\mathrm{CP}$ violation in $B_d\to J/\psi K_S$ decays and from $B_s-B_s$ mixing. If there is significant new physics in $B-\overline{B}$ mixing, then those experiments will not yield the correct values for the CKM matrix elements. As a result, a qualitative signal of new physics may appear in the $\mathrm{CP}$ violation of decays such as $B_d\to {\pi }^{+}{\pi }^{-}.$

• Received 11 February 2000

DOI:https://doi.org/10.1103/PhysRevD.62.014018