Measurement of the CP-violating phase ϕ_s in the B_s ⁰→J/ψϕ(1020)→μ⁺μ⁻K⁺K⁻ channel in proton-proton collisions at s=13TeV

The CP -violating weak phase ϕ_s and the decay width difference ΔΓ_s between the light and heavy B_s ⁰ mass eigenstates are measured with the CMS detector at the LHC in a sample of 48500 reconstructed B_s ⁰→J/ψϕ(1020)→μ⁺μ⁻K⁺K⁻ events. The measurement is based on a data sample corresponding to an integrated luminosity of 96.4fb⁻¹, collected in proton-proton collisions at s=13TeV in 2017–2018. To extract the values of ϕ_s and ΔΓ_s, a time-dependent and flavor-tagged angular analysis of the μ⁺μ⁻K⁺K⁻ final state is performed. The analysis employs a dedicated tagging trigger and a novel opposite-side muon flavor tagger based on machine learning techniques. The measurement yields ϕ_s=−11±50(stat)±10(syst)mrad and ΔΓ_s=0.114±0.014(stat)±0.007(syst)ps⁻¹, in agreement with the standard model predictions. When combined with the previous CMS measurement at s=8TeV, the following values are obtained: ϕ_s=−21±44(stat)±10(syst)mrad, ΔΓ_s=0.1032±0.0095(stat)±0.0048(syst)ps⁻¹, a significant improvement over the 8 TeV result.