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Compact Muon Solenoid
LHC, CERN

CMS-PAS-BPH-23-004
Measurement of time-dependent CP violation in B0sJ/ψϕ(1020) decays with the CMS detector
Abstract: A study of CP violation in B0sJ/ψϕ(1020) decays is presented, based on the data collected by the CMS experiment at the LHC. The measurement is based on a data sample of roughly 491 000 reconstructed signal events corresponding to an integrated luminosity of 96.5 fb1, collected in proton-proton collisions at 13 TeV in 2017-2018. A time- and flavor-dependent angular analysis of the μ+μK+K final state is performed to extract the values of the CP-violating phase ϕs, the decay width difference (ΔΓs), and absolute mass difference (Δms) between the light and heavy B0s mass eigenstates, their average decay width Γs, and the direct CP violation parameter |λ|. The analysis utilizes a pioneering inclusive flavor tagging framework based on state-of-the-art machine learning techniques, achieving exceptional performance by exploiting both opposite-side and same-side information. The measurement yields ϕs=73 ± 23 (stat) ± 7 (syst) mrad, ΔΓs= 0.0761 ± 0.0043 (stat) ± 0.0019 (syst) ps1, Δms= 17.757 ± 0.035 (stat) ± 0.017 (syst)  ps1, Γs= 0.6613 ± 0.0015 (stat) ± 0.0028 (syst) ps1, and |λ|= 1.011 ± 0.014 (stat) ± 0.012 (syst). These results exhibit a level of precision on par with the most precise single measurements to date and agree with the standard model predictions. A combination with the previous CMS results obtained at 8 TeV is also performed, yielding ϕs=74 ± 23 mrad and ΔΓs= 0.0780 ± 0.0045 ps1. The weak phase ϕs is found different from zero by 3.2 standard deviations, indicating evidences for CP violation in B0sJ/ψK+K decays.
CMS Publications
Compact Muon Solenoid
LHC, CERN