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

Abstract

© 2021 The Author(s). The CP -violating weak phase ϕ and the decay width difference ΔΓ between the light and heavy B mass eigenstates are measured with the CMS detector at the LHC in a sample of 48500 reconstructed B →J/ψϕ(1020)→μ μ K K events. The measurement is based on a data sample corresponding to an integrated luminosity of 96.4fb , collected in proton-proton collisions at s=13TeV in 2017–2018. To extract the values of ϕ and ΔΓ , 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 =−11±50(stat)±10(syst)mrad and ΔΓ =0.114±0.014(stat)±0.007(syst)ps , in agreement with the standard model predictions. When combined with the previous CMS measurement at s=8TeV, the following values are obtained: ϕ =−21±44(stat)±10(syst)mrad, ΔΓ =0.1032±0.0095(stat)±0.0048(syst)ps , a significant improvement over the 8 TeV result.