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).

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