The leptonic and inclusive hadronic decay branching fractions of the $W$ boson are measured using proton-proton collision data collected at $\sqrt{s}=13\mathrm{TeV}$ by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of $35.9{\mathrm{fb}}^{-1}$. 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 $|V_{cs}|=0.967\pm 0.011$, and the strong coupling constant at the $W$ boson mass scale, ${\alpha }_{\mathrm{S}}(m_W^2)=0.095\pm 0.033$.

• Received 19 January 2022
• Accepted 28 February 2022

DOI:https://doi.org/10.1103/PhysRevD.105.072008

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