First observation of the decay B<inf>s</inf>⁰ → φ K̄*⁰

The first observation of the decay B _s ⁰ → φK̄* ⁰ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb ^-1 of pp collisions at √s = 7 TeV, collected with the LHCb detector. A yield of 30 ± 6 B _s ⁰ → (K ⁺K ^-)(K ^-π ⁺) decays is found in the mass windows 1012:5 < M(K ⁺K) < 1026:5MeV/c ² and 746 < M(K ^-π ⁺) < 1046MeV/c ². The signal yield is found to be dominated by B _s ⁰ → φK̄* ⁰ decays, and the corresponding branching fraction is measured to be B(B _s ⁰ → φK̄* ⁰) = (1:10 ± 0:24 (stat) ± 0:14 (syst) ± 0:08 (f _d/f _s)) × 10 ^-6, where the uncertainties are statistical, systematic and from the ratio of fragmentation fractions f _d/f _s which accounts for the different production rate of B ⁰ and B _s ⁰ mesons. The significance of B _s ⁰ → φK̄* ⁰ signal is 6.1 standard deviations. The fraction of longitudinal polarization in B _s ⁰ → φK̄* ⁰ decays is found to be f ₀ = 0:51 ± 0:15 (stat) ± 0:07 (syst). Copyright CERN.