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 3fb−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 ACP(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 beACP(K−K+)=(0.14±0.15(stat)±0.10(syst))%. A combination of this result with previous LHCb measurements yieldsACP(K−K+)=(0.04±0.12(stat)±0.10(syst))%,ACP(π−π+)=(0.07±0.14(stat)±0.11(syst))%. These are the most precise measurements from a single experiment. The result for ACP(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.