CMS measures W boson mass with record precision at 13 TeV

CMS analyzed over 100 million W→μν decays from 2016 pp collisions at 13 TeV to extract mW using a highly granular, in-situ template fit of the muon pT, eta and charge distributions, aided by state-of-the-art NNLO+N3LL theory and data-driven PDFs; the result mW = 80,360.2 ± 9.9 MeV agrees with the Standard Model and helps address the prior CDF tension, with an additional W+ vs W− mass difference measurement of 57.0 ± 30.3 MeV. The analysis validates via Z-boson mass checks and a W-like mZ cross-check, and features robust muon momentum scale and hadronic recoil calibrations.