Measurement of CP observables in B 0 → DK ∗0 with D →K + K −

Abstract

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 B¯¯¯¯0→DK¯¯¯¯¯∗0

decay rates, with the neutral D meson in the CP-even final state K + K −, is found to be $ \mathcal{A}_d^{KK }=-0.45\pm 0.23\pm 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 $ \mathcal{R}_d^{KK }=1.36_{-0.32}^{+0.37}\pm 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 B¯¯¯¯0s→DK∗0 decay with D→K + K −, arealsoreported.