Measurement of the CP-violating phase ϕs in the Bs0→J/ψϕ(1020)→μ+μK+K channel in proton-proton collisions at √s=13 TeV

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  • ATLAS Collaboration

Colleges, School and Institutes


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+μK+K events. The measurement is based on a data sample corresponding to an integrated luminosity of 96.4 fb-1, collected in proton-proton collisions at √s=13 TeV in 2017–2018. To extract the values of ϕs and ΔΓs, a time-dependent and flavor-tagged angular analysis of the μ+μK+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=8 TeV , 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.

Bibliographic note

51 pages in total, author list starting page 35, 12 figures, 11 tables, submitted to EPJC. All figures including auxiliary figures are available at


Original languageEnglish
Article number136188
Number of pages27
JournalPhys. Lett. B
Early online date3 Mar 2021
Publication statusE-pub ahead of print - 3 Mar 2021


  • CMS, Physics, Oscillations, B physics