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arXiv · 2007.02434

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

CMS Collaboration
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Abstract

The $CP$-violating weak phase $ϕ_\mathrm{s}$ and the decay width difference $ΔΓ_\mathrm{s}$ between the light and heavy B$^0_\mathrm{s}$ mass eigenstates are measured with the CMS detector at the LHC in a sample of 48 500 reconstructed B$^0_\mathrm{s}$ $\to$ J$/ψ\, ϕ$(1020) $\to$ $μ^+μ^-$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 $ϕ_\mathrm{s}$ and $ΔΓ_\mathrm{s}$, a time-dependent and flavor-tagged angular analysis of the $μ^+μ^-$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 $ϕ_\mathrm{s} = -$11 $\pm$ 50 (stat) $\pm$ 10 (syst) mrad and $ΔΓ_\mathrm{s} =$ 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: $ϕ_\mathrm{s} = -$21 $\pm$ 44 (stat) $\pm$ 10 (syst) mrad, $ΔΓ_\mathrm{s} =$ 0.1032 $\pm$ 0.0095 (stat) $\pm$ 0.0048 (syst) ps$^{-1}$, a significant improvement over the 8 TeV result.

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CMS Collaboration. 2021-03-11. Measurement of the $CP$-violating phase $ϕ_\mathrm{s}$ in the B$^0_\mathrm{s}$ $\to$ J$/ψ\, ϕ$(1020) $\to$ $μ^+μ^-$K$^+$K$^-$ channel in proton-proton collisions at $\sqrt{s} =$ 13 TeV. https://doi.org/10.1016/j.physletb.2021.136188

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