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

A time- and flavor-integrated amplitude analysis of B0 and Bs0 decays to the (K+π-)(K-π+) final state in the K*(892)0K¯*(892)0 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 Bs0 decays are measured relative to the B0→D-π+ and Bs0→Ds-π+ modes, respectively. The corresponding longitudinal polarization fractions are found to be fLd=0.600±0.022±0.017 and fLs=0.159±0.010±0.007, where the uncertainties are statistical and systematic, respectively. The theory-motivated ratio of the squared Bs0 to B0 longitudinally polarized decay amplitudes is found to be LK*0K¯*0=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.