Measurement of CP asymmetry in D⁰ → K⁻K⁺ decays

A measurement of the time-integrated CP asymmetry in the Cabibbo-suppressed decay D⁰→K⁻K⁺ is performed using pp collision data, corresponding to an integrated luminosity of 3 fb⁻¹, collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in D^⁎+→D⁰π⁺ and D^⁎−→D‾⁰π⁻ decays. The time-integrated CP asymmetry A_CP(K⁻K⁺) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D⁰→K⁻π⁺, D⁺→K⁻π⁺π⁺ and D⁺→K‾⁰π⁺ decays used as calibration channels. It is found to be A_CP(K⁻K⁺)=(0.14±0.15 (stat)±0.10 (syst))%. A combination of this result with previous LHCb measurements yields A_CP(K⁻K⁺)=(0.04±0.12 (stat)±0.10 (syst))%,A_CP(π⁻π⁺)=(0.07±0.14 (stat)±0.11 (syst))%. These are the most precise measurements from a single experiment. The result for A_CP(K⁻K⁺) is the most precise determination of a time-integrated CP asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.