First Observation of the Decay anti-B0s → D0 K∗0 and a Measurement of the Ratio of Branching Fractions B(anti-B0s → D0 K∗0)/B(anti-B0 → D0 ρ0)

The first observation of the decay B0s → D0 K∗0 using pp data collected by the LHCb detector at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 36 pb^−1, is reported. A signal of 34.4 ± 6.8 events is obtained and the absence of signal is rejected with a statistical significance of more than nine standard deviations. The anti-B0s → D0 K∗0 branching fraction is measured relative to that of anti-B0 → D0 ρ0: B(anti-B0s → D0 K∗0)/B(anti-B0 → D0 ρ0) = 1.48 ± 0.34 ± 0.15 ± 0.12, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the B0 and B0s hadronisation fractions.