This talk will describe the measurement of CP violating parameters in the decay process of BsO→J/ψ(→μ+μ−)ϕ(→K+K−). The study is based on proton-proton collision data collected during 2017–2018 by the CMS experiment at √s=13 TeV, corresponding to an integrated luminosity of 96.4 fb−1. The angular analysis of the decay process mainly focuses on the measurement of the weak phase ϕs; it also extracts the oscillation frequency (Δms), the difference in the decay width between the Bs mass eigenstates (ΔΓs), and the direct CP-violating parameter (λ). The results of the measurement at 13 TeV are combined with those at 8 TeV leading to significant improvements.
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