Measurement of CP observables in B ⁰ → DK ^{â̂ - 0} with D →k ⁺ K ^- 0 w

The decay B ⁰ → DK ^*0 and the charge conjugate mode are studied using 1.0 fb^-1 of pp collision data collected by the LHCb experiment at √S=7 TeV in 2011. The CP asymmetry between the B ⁰ → DK ^*0 and the ̄0 to D̄K^*0 decay rates, with the neutral D meson in the CP-even final state K ⁺ K ^-, is found to be A^KK _d =-0.45±0.23±0.02, where the first uncertainty is statistical and the second is systematic. In addition, favoured B ⁰ → DK ^*0 decays are reconstructed with the D meson in the non-CP eigenstate K ⁺π^-. The ratio of the B-flavour averaged decay rates in D decays to CP and non-CP eigenstates is measured to be R^KK_d =1.36^+0.37_-0.32± 0.07, where the ratio of the branching fractions of D ⁰ → K ^-π⁺ to D ⁰ → K ⁺ K ^- decays is included as multiplicative factor. The CP asymmetries measured with two control channels, the favoured B ⁰ → DK ^*0 decay with D → K ⁺π^- and the ̄B⁰_s0 → DK^*0 decay with D→K ⁺ K ^-, arealsoreported.