Measurement of the branching fractions and longitudinal polarizations of B⁰₍ₛ₎ → K*⁰ K⁻ *⁰ decays

A time- and flavor-integrated amplitude analysis of B0 and B0s decays to the ðKþπ−ÞðK−πþÞ final state in the Kð892Þ0K¯ ð892Þ0 region is presented, using pp collision data recorded with the LHCb detector in 2011–2018, corresponding to an integrated luminosity of 9 fb−1. The branching fractions of the B0 and B0s decays are measured relative to the B0 → D−πþ and B0s → D−s πþ modes, respectively. The corresponding longitudinal polarization fractions are found to be fd L ¼ 0.600  0.022  0.017 and fs L ¼ 0.159  0.010  0.007, where the uncertainties are statistical and systematic, respectively. The theory-motivated ratio of the squared B0s to B0 longitudinally polarized decay amplitudes is found to be LK0K¯ 0 ¼ 4.92  0.55  0.48  0.02  0.10, where the uncertainties are statistical, systematic, due to uncertainty of external mass and lifetime measurements, and due to knowledge of the fragmentation fraction ratio, respectively. This confirms the previously reported tension between experimental determinations and theoretical predictions of longitudinal polarization in B → VV decays at the level of 4.4 standard deviations. (LHCb Collaboration)