Measurement of the CP-violating phase phi_s in the B0s -> J/psi phi(1020) -> mu+mu- K+K- channel in proton-proton collisions at sqrt(s) = 13 TeV

The CP -violating weak phase φs and the decay width difference ΔΓs between the light and heavy B0s mass eigenstates are measured with the CMS detector at the LHC in a sample of 48500 reconstructed B0s→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 φs and ΔΓs, 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 φs=−11±50(stat)±10(syst)mrad and ΔΓs=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: φs=−21±44(stat)±10(syst)mrad, ΔΓs=0.1032±0.0095(stat)±0.0048(syst)ps−1, a significant improvement over the 8 TeV result.