Measurement of CP asymmetries and polarisation fractions in B s 0 → K ∗ 0 K ¯ ∗ 0 $$ {B}_s^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ decays

An angular analysis of the decay B s 0 → K ∗ 0 K ¯ ∗ 0 $$ {B}_s^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ is performed using pp collisions corresponding to an integrated luminosity of 1 . 0 fb −1 collected by the LHCb experiment at a centre-of-mass energy s = 7 $$ \sqrt{s}=7 $$ TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction f L = 0 . 201 ± 0 . 057 (stat . ) ± 0 . 040 (syst . ) for the B s 0 → K ∗ 892 0 K ¯ ∗ 892 0 $$ {B}_s^0\to {K}^{\ast }{(892)}^0{\overline{K}}^{\ast }{(892)}^0 $$ decay. A large scalar contribution from the K 0 ∗ (1430) and K 0 ∗ (800) resonances is found, allowing the determination of additional CP asymmetries. Triple product and direct CP asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction ℬ B s → K ∗ 892 0 K ¯ ∗ 892 0 $$ \mathrm{\mathcal{B}}\left({B}_s\to {K}^{\ast }{(892)}^0{\overline{K}}^{\ast }{(892)}^0\right) $$ is measured to be (10 . 8 ± 2 . 1 (stat . ) ± 1 . 4 (syst . ) ± 0 . 6 ( f d /f s )) × 10 −6 .