Measurement of CP asymmetry in D⁰ -> K^-K⁺ and D⁰ -> π^-π⁺ decays

Time-integrated CP asymmetries in D-0 decays to the final states K- K+ and pi(-) pi(+) 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 D-0 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 beΔACP = ACP(K-K+) - ACP(π-π+) = (+0.14 ± 0.16 (stat) ± 0.08 (syst))% .A measurement of A(CP)(K- K+) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D decays. It is found to beA(CP)(K- K+) = (-0.06 +/- 0.15 (stat) +/- 0.10 (syst))% ,where the correlation coefficient between Delta A(CP) and A(CP)(K- K+) is rho = 0.28. By combining these results, the CP asymmetry in the D-0 -> pi(-) pi(+) channel is A(CP)(pi(-) pi(+)) = (-0.20 +/- 0.19 (stat) +/- 0.10 (syst))%.