Measurement of D⁰ ‒ D¯⁰ mixing and search for CP violation with D⁰ → K⁺ π⁻ decays

A measurement of the time-dependent ratio of the D0→K+π- to D¯0→K+π- decay rates is reported. The analysis uses a sample of proton-proton collisions corresponding to an integrated luminosity of 6 fb-1 recorded by the LHCb experiment from 2015 through 2018 at a center-of-mass energy of 13 TeV. The D0 meson is required to originate from a D∗(2010)+→D0π+ decay, such that its flavor at production is inferred from the charge of the accompanying pion. The measurement is performed simultaneously for the K+ π- and K- π+ final states, allowing both mixing and CP-violation parameters to be determined. The value of the ratio of the decay rates at production is determined to be RKπ=(343.1±2.0)×10-5. The mixing parameters are measured to be cKπ=(51.4±3.5)×10-4 and cKπ′=(13±4)×10-6, where RKπcKπ is the linear coefficient of the expansion of the ratio as a function of decay time in units of the D0 lifetime, and cKπ′ is the quadratic coefficient, both averaged between the K+ π- and K- π+ final states. The precision is improved relative to the previous best measurement by approximately 60%. No evidence for CP violation is found. [The LHCb Collaboration]