Measurement of the $CP$-violating phase ${\varphi }_{\mathrm{s}}$ in the B${}_{\mathrm{s}}^0$ $\to$ J$/\psi \varphi$(1020) $\to$ ${\mu }^{+}{\mu }^{-}$K${}^{+}$K${}^{-}$ channel in proton-proton collisions at $\sqrt{s}=$ 13 TeV

Abstract

The $CP$-violating weak phase ${\varphi }_{\mathrm{s}}$ and the decay width difference $\Delta {\Gamma }_{\mathrm{s}}$ between the light and heavy B${}_{\mathrm{s}}^0$ mass eigenstates are measured with the CMS detector at the LHC in a sample of 48 500 reconstructed B${}_{\mathrm{s}}^0$ $\to$ J$/\psi \varphi$(1020) $\to$ ${\mu }^{+}{\mu }^{-}$K${}^{+}$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 $\sqrt{s}=$ 13 TeV in 2017-2018. To extract the values of ${\varphi }_{\mathrm{s}}$ and $\Delta {\Gamma }_{\mathrm{s}}$, a time-dependent and flavor-tagged angular analysis of the ${\mu }^{+}{\mu }^{-}$K${}^{+}$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 ${\varphi }_{\mathrm{s}}=-$11 $\pm$ 50 (stat) $\pm$ 10 (syst) mrad and $\Delta {\Gamma }_{\mathrm{s}}=$ 0.114 $\pm$ 0.014 (stat) $\pm$ 0.007 (syst) ps${}^{-1}$, in agreement with the standard model predictions. When combined with the previous CMS measurement at $\sqrt{s}=$ 8 TeV, the following values are obtained: ${\varphi }_{\mathrm{s}}=-$21 $\pm$ 44 (stat) $\pm$ 10 (syst) mrad, $\Delta {\Gamma }_{\mathrm{s}}=$ 0.1032 $\pm$ 0.0095 (stat) $\pm$ 0.0048 (syst) ps${}^{-1}$, a significant improvement over the 8 TeV result.

arXiv commentReplaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/BPH-20-001 (CMS Public Pages)

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