Measurement of the ${B}_{s}^{0}\to J/{\mathrm{\psi K}}_{S}^{0}$ effective lifetime from proton-proton collisions at $\sqrt{s}$ = 13 TeV

The effective lifetime of the ${B}_{s}^{0}$ meson in the decay ${B}_{s}^{0}\to J/{\mathrm{\psi K}}_{S}^{0}$ is measured using data collected during 2016–2018 with the CMS detector in $\sqrt{s}$ = 13 TeV proton-proton collisions at the LHC, corresponding to an integrated luminosity of 140 fb −1. The effective lifetime is determined by performing a two-dimensional unbinned maximum likelihood fit to the ${B}_{s}^{0}$ meson invariant mass and proper decay time distributions. The resulting value of 1.59 ± 0.07(stat) ± 0.03(syst) ps is the most precise measurement to date and is in good agreement with the expected value.