Measurement of strong phase in $D^0\to K\pi$ decay at BESIII

Based on 2.92 fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data collected with the BESIII detector at $\sqrt{s}$ = 3.773 GeV, we measured the asymmetry ${\mathcal{A}}_{CP\to K\pi }$ of the branching fractions of $D^{CP\pm}\to K^-\pi^+$($D^{CP\pm}$arethe$CP$-oddand$CP$-eveneigenstates)tobe$(12.77\pm1.31^{+0.33}{-0.31})%$\mathrm{.}$$\mathcal{A}${CP\to K\pi}$ is used to extract the strong phase difference ${\delta }_{K\pi }$ between the doubly Cabibbo-suppressed process $\bar{D}{}^0\to K^{-}{\pi }^{+}$ and Cabibbo-favored $D^0\to K^{-}{\pi }^{+}$. By taking inputs of other parameters in world measurements, we obtain $\cos {\delta }_{K\pi }=1.03\pm 0.12\pm 0.04\pm 0.01$. This is the most accurate result of $\cos {\delta }_{K\pi }$ to date and can improve the world constrains on the mixing parameters and on $\gamma \mathrm{/}{\varphi }_3$ in the CKM matrix.