Measurement of CP Observables in B0 → D K∗0 with D → K+ K−

The decay B0 → D K*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 B0 → D K*0 and the anti-B0 → D anti-K∗0 decay rates, with the neutral D meson in the CP-even final state K+ K−, is found to be A_d^KK = −0.45 ± 0.23 ± 0.02, where the first uncertainty is statistical and the second is systematic. In addition, favoured B0 → D K*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_d^KK = 1.36(−0.32)(+0.37) ± 0.07, where the ratio of the branching fractions of D0 → K− π+ to D0 → K+ K− decays is included as multiplicative factor. The CP asymmetries measured with two control channels, the favoured B0 → D K*0 decay with D → K+ π− and the anti-B0s → D K∗0 decay with D → K+ K−, are also reported.