Impact of tag-side interference on time-dependent CP asymmetry measurements using coherent $B^0{B}^0$ pairs

Interference between Cabibbo-Kobayashi-Maskawa (CKM) favored $\overrightarrow{b}cūd$ and doubly-CKM-suppressed $\overline{b}\to ūc\overline{d}$ amplitudes in final states used for B-flavor tagging gives deviations from the standard time evolution assumed in CP-violation measurements at B factories producing coherent $B^0{B}^0$ pairs. We evaluate these deviations for the standard time-dependent CP-violation measurements, the uncertainties they introduce in the measured quantities, and give suggestions for minimizing them. The uncertainty in the measured CP asymmetry for CP eigenstates is $\approx 2\%$ or less. The time-dependent analysis of $D^{*}\pi ,$ proposed for measuring $\sin (2\mathrm{}\beta +\gamma ),$ must incorporate possible tag-side interference, which could produce asymmetries as large as the expected signal asymmetry.