Measurement of the B⁰ₛ → J/ψK⁰ₛ effective lifetime from proton-proton collisions at √s = 13 TeV

The effective lifetime of the B⁰ₛ meson in the decay B⁰ₛ → J/ψK⁰ₛ is measured using data collected during 2016–2018 with the CMS detector in √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 B⁰ₛ 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.