Observation of B 0 s → ¯ D * 0 ϕ and search for B 0 → ¯ D 0 ϕ decays

The first observation of the B 0 s → ¯ D * 0 ϕ decay is reported, with a significance of more than seven standard deviations, from an analysis of p p collision data corresponding to an integrated luminosity of 3     fb − 1 , collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The branching fraction is measured relative to that of the topologically similar decay B 0 → ¯ D 0 π + π − and is found to be B ( B 0 s → ¯ D * 0 ϕ ) = ( 3.7 ± 0.5 ± 0.3 ± 0.2 ) × 1 0 − 5 , where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the B 0 → ¯ D 0 π + π − decay. The fraction of longitudinal polarization in this decay is measured to be f L = ( 73 ± 15 ± 4 ) % . The most precise determination of the branching fraction for the B 0 s → ¯ D 0 ϕ decay is also obtained, B ( B 0 s → ¯ D 0 ϕ ) = ( 3.0 ± 0.3 ± 0.2 ± 0.2 ) × 1 0 − 5 . An upper limit, B ( B 0 → ¯ D 0 ϕ ) < 2.0 ( 2.3 ) × 1 0 − 6 at 90% (95%) confidence level is set. A constraint on the ω − ϕ mixing angle δ is set at | δ | < 5.2 ° (5.5°) at 90% (95%) confidence level.