CMS-PAS-BPH-20-001

CMS-PAS-BPH-20-001
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 TeV
CMS Collaboration
March 2020

Abstract: 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 fb$^{-1}$, collected in proton-proton collisions at a center-of-mass energy of 13 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 (stat) $\pm$ 0.010 (syst) rad, and $\Delta\Gamma_{\text{s}} =$ 0.114 $\pm$ 0.014 (stat) $\pm$ 0.007 (syst) 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 rad, $\Delta\Gamma_{\text{s}} = $ 0.1074 $\pm$ 0.0097 ps$^{-1}$, a significant improvement over the 8 TeV result.
Links: CDS record (PDF) ; inSPIRE record ; HepData record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 816 (2021) 136188. The superseded preliminary plots can be found here.

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