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

Abstract

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 $D^{CP\pm}\to K^-\pi^+$ ($D^{CP\pm}$ are the $CP$-odd and $CP$-even eigenstates) to be $(12.77\pm1.31^{+0.33}_{-0.31})\%$. $\mathcal{A}_{CP\to K\pi}$ is used to extract the strong phase difference $\delta_{K\pi}$ between the doubly Cabibbo-suppressed process $\overline{D}{}^{0}\to K^- \pi^+$ and Cabibbo-favored $D^0\to K^- \pi^+$. By taking inputs of other parameters in world measurements, we obtain $\cos\delta_{K\pi} = 1.03\pm0.12\pm0.04\pm0.01$. 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 $\gamma/\phi_3$ in the CKM matrix.