Observation of the decay Bs0→D¯0ϕ

First observation of the decay Bos → D-oφ is reported using pp collision data, corresponding to an integrated luminosity of 1.0 fb−1, collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. The significance of the signal is 6.5 standard deviations. The branching fraction is measured relative to that of the decay Bos → D-oK-*o to be B(B0s →D0φ) B(B0s →D0K∗0) = 0.069±0.013 (stat)±0.007 (syst). The first measurement of the ratio of branching fractions for the decays B0s → D0K∗0 and B0 → D0K∗0 is found to be B(B0s →D0K∗0) B(B0→D0K∗0) = 7.8±0.7 (stat)± 0.3 (syst)± 0.6 ( fs/ fd), where the last uncertainty is due to the ratio of the B0s and B0 fragmentation fractions.