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

Abstract

Time-integrated CP asymmetries in D0 decays to the final states K−K+ and π −π + are measured using proton-proton collisions corresponding to 3 fb−1 of integrated luminosity collected at centre-of-mass energies of 7 TeV and 8 TeV. The D0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in CP asymmetries between the two final states is measured to be ∆ACP = ACP (K−K+) − ACP (π −π +) = (+0.14 ± 0.16 (stat) ± 0.08 (syst))% . A measurement of ACP (K−K+) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D decays. It is found to be ACP (K−K+) = (−0.06 ± 0.15 (stat) ± 0.10 (syst))% , where the correlation coefficient between ∆ACP and ACP (K−K+) is ρ = 0.28. By combining these results, the CP asymmetry in the D0 → π −π + channel is ACP (π −π +) = (−0.20 ± 0.19 (stat) ± 0.10 (syst))%.