Improved Measurement of CP Violation Parameters in B 0 s →J/ψK + K − Decays in the Vicinity of the ϕ(1020) Resonance

• Published in: Physical review letters 2024, Vol.132 (5)
• Main Authors: Aaij, R., Adlarson, Patrik, Eklund, Lars, Kupsc, Andrzej, Zunica, G.
• Format: Article
• Language: English
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.132.051802

The decay-time-dependent CP asymmetry in B 0 s →J/ψ(→μ + μ − )K + K − decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6  fb −1 , collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 B 0 s signal decays with an invariant K + K − mass in the vicinity of the ϕ(1020) resonance, the CP-violating phase ϕs is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the B 0 s −¯B 0 s system, ΔΓ s , and the difference of the average B 0 s and B 0 meson decay widths, Γ s −Γ d . The values obtained are ϕ s =−0.039±0.022±0.006  rad, ΔΓ s =0.0845±0.0044±0.0024  ps −1 , and Γ s −Γ d =−0.0056 +0.0013 −0.0015 ±0.0014  ps −1 , where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ϕs is also measured independently for each polarization state of the K + K − system and shows no evidence for polarization dependence.