Measurement of the CP-violating phase ϕs in the Bs0→ J/ψ ϕ(1020) →μ+μ−K+K− channel in proton-proton collisions at √s = 13 TeV
The CP -violating weak phase ϕs and the decay width difference ΔΓs between the light and heavy Bs0 mass eigenstates are measured with the CMS detector at the LHC in a sample of 48500 reconstructed Bs0→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.
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