Abstract: The mass of theWboson, a mediator of the weak force between elementary particles, is tightly constrainedby the symmetries of the standard model of particle physics. The Higgs boson was the last missingcomponent of the model. After observation of the Higgs boson, a measurement of theWboson mass provides astringent test of the model. We measure theWboson mass,MW, using data corresponding to 8.8 inversefemtobarns of integrated luminosity collected in proton-antiproton collisions at a 1.96 tera?electronvolt center-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. A sample of approximately4 millionWboson candidates is used to obtainMW¼80;433:5T6:4statT6:9syst¼80;433:5T9:4MeV=c2,the precision of which exceeds that of all previous measurements combined (stat, statistical uncertainty;syst, systematic uncertainty; MeV, mega?electron volts;c, speed of light in a vacuum). This measurementis in significant tension with the standard model expectation.

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