Measurement of $CP$ asymmetries and polarisation fractions in $B_s^0\to K^{\ast 0}\bar{K}{}^{\ast 0}$ decays

An angular analysis of the decay $B_s^0\to K^{\ast 0}\bar{K}{}^{\ast 0}$ 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 $f_L=0.201\pm 0.057(stat\mathrm{.})\pm 0.040(syst\mathrm{.})$ for the $B_s^0 \rightarrow K^(892)^0 \bar{K}{}^(892)^0$decay\mathrm{.}Alargescalarcontributionfromthe$K^{}_{0}(1430)$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 $$\mathcal{B}$(B_s^0 \rightarrow K^(892)^0 \bar{K}{}^(892)^0)$ismeasuredtobe$(10.8 \pm 2.1 {\ \rm (stat.)} \pm 1.4 {\ \rm (syst.)} \pm 0.6 \ (f_d/f_s) ) \times 10^{-6}$.