Observation of CP violation in charm decays

A search for charge-parity (CP) violation in D⁰→K^-K⁺ and D⁰→π^-π⁺ decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb^-1 collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D^∗(2010)⁺→D⁰π⁺ decays or from the charge of the muon in B̅→D⁰μ^-ν̄_μX decays. The difference between the CP asymmetries in D⁰→K^-K⁺ and D⁰→π^-π⁺ decays is measured to be ΔA_CP=[-18.2±3.2(stat)±0.9(syst)]×10^-4 for π-tagged and ΔA_CP=[-9±8(stat)±5(syst)]×10^-4 for μ-tagged D⁰ mesons. Combining these with previous LHCb results leads to ΔA_CP=(-15.4±2.9)×10^-4, where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons.