First observation of the decay $B_s^0\to \phi \overline{K}{*^0}$

Abstract

The first observation of the decay $B_s^0\to \phi \overline{K}{*^0}$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb⁻¹ of pp collisions at $\sqrt{s}=7$ TeV, collected with the LHCb detector. A yield of 30 ± 6 $B_s^0\to \left( {{K^{+}}{K^{-}}} \right)\left( {{K^{-}}{\pi^{+}}} \right)$ decays is found in the mass windows 1012.5 < M (K ⁺ K ⁻) < 1026.5 MeV/c ² and 746 < M(K ⁻ π ⁺) < 1046 MeV/c ². The signal yield is found to be dominated by $B_s^0\to \phi \overline{K}{*^0}$ decays, and the corresponding branching fraction is measured to be $\mathcal{B}\left( {B_s^0\to \phi \overline{K}{*^0}} \right)$ = (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 $B_s^0\to \phi \overline{K}{*^0}$ signal is 6.1 standard deviations. The fraction of longitudinal polarization in $B_s^0\to \phi \overline{K}{*^0}$ decays is found to be f ₀ = 0.51 ± 0.15 (stat) ± 0.07 (syst).