Precision measurement of the W boson decay branching fractions in proton-proton collisions at $\sqrt{s}=$ 13 TeV

Abstract

The leptonic and inclusive hadronic decay branching fractions of the W boson are measured using proton-proton collision data collected at $\sqrt{s}=$ 13 TeV by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 35.9 fb${}^{-1}$. Events characterized by the production of one or two W bosons are selected and categorized based on the multiplicity and flavor of reconstructed leptons, the number of jets, and the number of jets identified as originating from the hadronization of b quarks. A binned maximum likelihood estimate of the W boson branching fractions is performed simultaneously in each event category. The measured branching fractions of the W boson decaying into electron, muon, and tau lepton final states are (10.83 $\pm$ 0.10)%, (10.94 $\pm$ 0.08)%, and (10.77 $\pm$ 0.21)%, respectively, consistent with lepton flavor universality for the weak interaction. The average leptonic and inclusive hadronic decay branching fractions are estimated to be (10.89 $\pm$ 0.08)% and (67.32 $\pm$ 0.23)%, respectively. Based on the hadronic branching fraction, three standard model quantities are subsequently derived: the sum of squared elements in the first two rows of the Cabibbo-Kobayashi-Maskawa (CKM) matrix ${\sum }_{ij}|V_{ij}{|}^2$ = 1.984 $\pm$ 0.021, the CKM element $|V_{\mathrm{cs}}|$ = 0.967 $\pm$ 0.011, and the strong coupling constant at the W boson mass scale, ${\alpha }_{\mathrm{S}}(m_{\mathrm{W}}^2)$ = 0.095 $\pm$ 0.033.

Replaced 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/SMP-18-011 (CMS Public Pages)

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