Improved model-independent determination of the strong-phase difference between D0 and D¯0→KS,L 0K+K- decays

We present a measurement of the strong-phase difference between D⁰ and D^¯0→K_S^{,L 0}K⁺K^- decays, performed through a study of quantum-entangled pairs of charm mesons. The measurement exploits a data sample equivalent to an integrated luminosity of 2.93 fb^-1 , collected by the BESIII detector in e⁺e^- collisions corresponding to the mass of the ψ (3770 ) resonance. The strong-phase difference is an essential input to the determination of the Cabibbo-Kobayashi-Maskawa (CKM) angle γ /ϕ₃ through the decay B^-→D K^-, where D can be either a D⁰ or a D^¯0 decaying to K_S^{,L 0}K⁺K^-. This is the most precise measurement to date of the strong-phase difference in these decays.