Measurement of the D →k⁻π⁺ strong phase difference in ψ(3770) →D⁰D̅⁰

We study D⁰D̅⁰ pairs produced in e⁺e⁻ collisions at √ s = 3.773 GeVusing a data sample of 2.92 fb⁻¹ collected with the BESIII detector. We measuredthe asymmetry A^CP _Kπ of the branching fractions of D → K⁻π⁺ in CP-odd and CP-even eigenstates to be (12.7 ± 1.3 ± 0.7) × 10⁻². A^CP _Kπ can be used to extract the strong phase difference δ_Kπ between the doubly Cabibbo-suppressed process D̅⁰ → K⁻π⁺ and the Cabibbo-favored process D⁰ → K⁻π⁺. Using world-average values of external parameters, we obtain cos δ_Kπ = 1.02 ±0.11 ±0.06 ±0.01. Here, the first and second uncertainties are statistical and systematic, respectively, while the third uncertainty arises from the external parameters. This is the most precise measurement of δ_Kπ to date.