Updated measurement of $CP$ violation and polarisation in $B_s^0\to J/\ddot{I}ˆ\overline{K}{}^{\ast }(892{)}^0$ decays

Abstract

A time-integrated angular analysis of the decay $B_s^0\to J/\ddot{I}ˆ\overline{K}{}^{\ast }(892{)}^0$, with $J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ and $\overline{K}{}^{\ast }(892{)}^0\to K^{-}\ddot{I}{€}^{+}$, 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 $13\text{TeV}$, corresponding to an integrated luminosity of $6{\text{fb}}^{-1}$. A simultaneous maximum-likelihood fit is performed to the angular distributions in bins of the $K^{-}\ddot{I}{€}^{+}$ mass. This fit yields measurements of the $CP$-averaged polarisation fractions and $CP$ asymmetries for the P-wave component of the $K^{-}\ddot{I}{€}^{+}$ system. The longitudinal and parallel polarisation fractions are determined to be $f_0=0.534\pm 0.012\pm 0.009$ and $f_{\parallel }=0.211\pm 0.014\pm 0.005$, 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 $B^0\to J/\ddot{I}ˆK^{\ast 0}$ decay, are combined with previous LHCb results, providing the most precise values for these observables to date.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/4457/ (LHCb public pages)