Measurement of the D→K−π+D→K−π+ strong phase difference in ψ(3770)→D0D¯0

We study D0D¯0 pairs produced in e+e−e+e− collisions at s=3.773 GeV using a data sample of 2.92 fb−1 collected with the BESIII detector. We measured the asymmetry AKπCP of the branching fractions of D→K−π+D→K−π+ in CP-odd and CP  -even eigenstates to be (12.7±1.3±0.7)×10−2(12.7±1.3±0.7)×10−2. AKπCP can be used to extract the strong phase difference δKπδKπ between the doubly Cabibbo-suppressed process D¯0→K−π+ and the Cabibbo-favored process D0→K−π+D0→K−π+. Using world-average values of external parameters, we obtain cosδKπ=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 δKπδKπ to date.