Precision measurement of the W boson decay branching fractions in proton-proton collisions at √s=13 TeV

The leptonic and inclusive hadronic decay branching fractions of the W boson are measured using proton-proton collision data collected at s 1⁄4 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 ð10.830.10Þ%, ð10.940.08Þ%, and ð10.770.21Þ%, respectively, consistent with lepton flavor universality for the weak interaction. The average leptonic and inclusive hadronic decay branching fractions are estimated to be ð10.89  0.08Þ% and ð67.32  0.23Þ%, respec- tively. 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 P ij jVijj2 1⁄4 1.984  0.021, the CKM element jVcsj 1⁄4 0.967  0.011, and the strong coupling constant at the W boson mass scale, αS ðm2W Þ 1⁄4 0.095  0.033.