Physicists zero in on the mass of the fundamental W boson particle

An international team including MIT physicists has published an ultraprecise measurement of the W boson mass using data from over 1 billion proton-proton collisions at CERN's Large Hadron Collider. Analyzing 100 million W boson decay events from the 2016 LHC run with the CMS detector, they determined the W boson mass to be 80360.2 ± 9.9 MeV — consistent with Standard Model predictions. This result directly contradicts the 2022 Fermilab CDF measurement, which found a significantly heavier mass and suggested possible 'new physics' beyond the Standard Model. The new CMS measurement, a product of 10 years of work and 4 billion simulated events, restores confidence in the Standard Model as an accurate description of fundamental particles and forces.