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

Abstract

An angular analysis of the decay ${B}_s^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0}$ 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 $\sqrt{s}=7$ 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 ${B}_s^0\to {K}^{\ast }{(892)}^0{\overline{K}}^{\ast }{(892)}^0$ 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 $\mathrm{\mathcal{B}}\left({B}_s\to {K}^{\ast }{(892)}^0{\overline{K}}^{\ast }{(892)}^0\right)$ is measured to be (10.8 ± 2.1 (stat.) ± 1.4 (syst.) ± 0.6 (f _d /f _s )) × 10⁻⁶.