Measurement of the $CP$ violating phase $\phi_{\text{s}}$ in the $\mathrm{B}_s \to \mathrm{J}/\psi\,\phi(1020) \to \mu^+\mu^-\,\mathrm{K}^+\mathrm{K}^-$ channel in proton-proton collisions at $\sqrt{s} = 13~\mathrm{TeV}$
2020.
The CMS collaboration

Abstract (data abstract)
The CP-violating weak phase $\phi_{\mathrm{s}}$ and the decay width difference $\Delta\Gamma_{\mathrm{s}}$ between the light and heavy $\mathrm{B}^0_\mathrm{s}$ mass eigenstates are measured with the CMS detector at the LHC in a sample of $48\,500$ reconstructed $\mathrm{B}^0_\mathrm{s}\to\mathrm{J /\psi}\,\mathrm{\phi(1020)} \to \mathrm{\mu^+}\mathrm{\mu^-}\,\mathrm{K^+}\mathrm{K^-}$ events. The measurement is based on a data sample corresponding to an integrated luminosity of $96.4\,\text{fb}^{-1}$, collected in proton-proton collisions at $\sqrt{s} = 13\,\text{TeV}$ in 2017--2018. To extract the values of $\phi_{\mathrm{s}}$ and $\Delta\Gamma_{\mathrm{s}}$, a time-dependent and flavor-tagged angular analysis of the $\mathrm{\mu^+}\mathrm{\mu^-}\mathrm{K^+}\mathrm{K^-}$ 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 $\phi_{\mathrm{s}} = -11 \pm 50\,\text{(stat)} \pm 10\,\text{(syst)}\,\text{mrad}$ and $\Delta\Gamma_{\mathrm{s}} = 0.114 \pm 0.014\,\text{(stat)} \pm 0.007\,\text{(syst)}\,\text{ps}^{-1}$, in agreement with the standard model predictions. When combined with the previous CMS measurement at $\sqrt{s} = 8\,\text{TeV}$, the following values are obtained: $\phi_{\mathrm{s}} = -21 \pm 45\,\text{mrad}$, $\Delta\Gamma_{\mathrm{s}} = 0.1073 \pm 0.0097\,\text{ps}^{-1}$, a significant improvement over the 8 TeV result.

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