A pioneering machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27$\,$000 tagged B$^0_\mathrm{s}$$\to$ J/$\psi\, \phi$(1020) decays from pp collisions at $\sqrt{s} =$ 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb$^{-1}$. A time- and flavor-dependent angular analysis of the $\mu^+\mu^-$K$^+$K$^-$ final state is used to measure parameters of the $\mathrm{B}^0_\mathrm{s}$-$\overline{\mathrm{B}}^0_\mathrm{s}$ system. The weak phase is measured to be $\phi_\mathrm{s}$ = $-$73 $\pm$ 23 (stat) $\pm$ 7 (syst) mrad, which, combined with a $\sqrt{s}$ = 8 TeV CMS result, gives $\phi_\mathrm{s}$ = $-$74 $\pm$ 23 mrad. This value differs from zero by 3.2 standard deviations, providing evidence for $CP$ violation in B$^0_\mathrm{s}$$\to$ J/$\psi\,\phi$(1020) decays. All measured physics parameters are found to agree with standard model predictions where available.
Measured values and uncertainties of the main parameters of interest, as obtained from the analysis to data at 13 TeV.
Values and uncertainties of the physics parameters obtained from the combination of the CMS 8 TeV and 13 TeV results using the BLUE method. The uncertainty includes both statistical and systematic sources.
Matrix of the correlations of the statistical uncertainties between pairs of physics parameters, as obtained from the analysis to data at 13 TeV.
The $CP$ violating weak phase $\phi_{\text{s}}$, and the decay width difference $\Delta\Gamma_{\text{s}}$ between the light and heavy $\mathrm{B_s}$ mass eigenstates are measured with the CMS detector at the LHC in a sample of reconstructed $\mathrm{B}_s \to \mathrm{J}/\psi\,\phi(1020) \to \mu^+\mu^-\,\mathrm{K}^+\mathrm{K}^-$ decays. The measurement is based on a data set corresponding to an integrated luminosity of $96.4\;\mathrm{fb}^{-1}$, collected in proton-proton collisions at a center-of-mass energy of $13\;\mathrm{TeV}$ in 2017-2018. To extract the values of $\phi_{\text{s}}$ and $\Delta\Gamma_{\text{s}}$, a time-dependent and flavor-tagged angular analysis of the $\mu^+\mu^-\,\mathrm{K}^+\mathrm{K}^-$ final state is performed. The analysis employs a novel opposite-side muon flavor tagger based on machine learning techniques, which, in conjunction with a dedicated tagging trigger, allowed to reach an unprecedented tagging power. The measurement yields $\phi_{\text{s}} = -0.011 \pm 0.050\,\mathrm{(stat)} \pm 0.010\,\mathrm{(syst)}\;\mathrm{rad}$, and $\Delta\Gamma_{\text{s}} = 0.114 \pm 0.014\,\mathrm{(stat)} \pm 0.007\,\mathrm{(syst)}\;\mathrm{ps}^{-1}$, in agreement with the standard model predictions. When combined with our previous measurement at a center-of-mass energy of 8 TeV, the following values are obtained: $\phi_{\text{s}} = -0.021 \pm 0.045\;\mathrm{rad}$, $\Delta\Gamma_{\text{s}} = 0.1074 \pm 0.0097\;\mathrm{ps}^{-1}$, a significant improvement over the 8 TeV result.
Results of the fit to the data at 13 TeV. Statistical uncertainties are obtained from the increase in $-\log{\mathcal{L}}$ by 0.5.
Values of parameter obtained combining the 13 TeV results with those obtained by CMS at 8 TeV.
Statistical correlation matrix of the physics parameters of interest, as obtained from the fit to data at 13 TeV.
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