Physicists on the CMS experiment at the LHC announced a new mass measurement of the W boson, using a novel technique for the most detailed investigation to date. After nearly a decade of analysis, they found the W boson’s mass to be 80,360.2 ± 9.9 MeV, consistent with the Standard Model’s prediction of 80,357 ± 6 MeV. This measurement, based on 300 million events from the 2016 LHC run and 4 billion simulated events, resolves a long-standing mystery. The CMS result is noted for its precision and unique determination of uncertainties, building on previous experiments’ work.