Observation of the decay Bs0→D-0φ

First observation of the decay Bs0→D-0φ 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 7TeV. The significance of the signal is 6.5 standard deviations. The branching fraction is measured relative to that of the decay Bs0→D-0K-*0 to beB(Bs0→D-0φ)B(Bs0→D-0K-*0)=0.069±0.013(stat)±0.007(syst). The first measurement of the ratio of branching fractions for the decays Bs0→D-0K-*0 and B0→D-0K*0 is found to beB(Bs0→D-0K-*0)B(B0→D-0K*0)=7.8±0.7(stat)±0.3(syst)±0.6(fs/fd), where the last uncertainty is due to the ratio of the Bs0 and B⁰ fragmentation fractions.