Updated measurement of CP violation and polarisation in $ {B}_s^0\to J/\psi {\overline{K}}^{\ast }{(892)}^0 $ decays

A time-integrated angular analysis of the decay ${B}_s^0\to J/\psi {\overline{K}}^{\ast }{(892)}^0$ , with J / ψ → μ + μ − and ${\overline{K}}^{\ast }{(892)}^0\to {K}^{-}{\pi}^{+}$ , is presented. The analysis employs a sample of proton-proton collision data collected by the LHCb experiment during 2015–2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb − 1 . A simultaneous maximum-likelihood fit is performed to the angular distributions in bins of the K − π + mass. This fit yields measurements of the CP -averaged polarisation fractions and CP asymmetries for the P-wave component of the K − π + system. The longitudinal and parallel polarisation fractions are determined to be f 0 = 0.534 ± 0.012 ± 0.009 and f || = 0.211 ± 0.014 ± 0.005, respectively, where the first uncertainty is statistical and the second is systematic. The CP asymmetries are measured with 3–7% precision and are found to be consistent with zero. These measurements, along with an updated determination of the branching fraction relative to the B 0 → J / ψK *0 decay, are combined with previous LHCb results, providing the most precise values for these observables to date.