Measurement of CP violation parameters and polarisation fractions in B s 0 → J / ψ K ¯ ∗ 0 $$ {\mathrm{B}}_{\mathrm{s}}^0\to \mathrm{J}/\psi {\overline{\mathrm{K}}}^{\ast 0} $$ decays

The first measurement of CP asymmetries in the decay $$ {B}_s^0\to J/\psi {\overline{\mathrm{K}}}^{\ast }{(892)}^0 $$ and an updated measurement of its branching fraction and polarisation fractions are presented. The results are obtained using data corresponding to an integrated luminosity of 3.0 fb −1 of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Together with constraints from B 0 → J/ψ ρ 0, the results are used to constrain additional contributions due to penguin diagrams in the CP -violating phase ϕ s , measured through B 0 decays to charmonium.