The CMS experiment at CERN's Large Hadron Collider has measured the mass of the W boson at 80,360.2 ± 9.9 MeV, a result published in Nature on April 8, 2026 [2]. The measurement agrees with the Standard Model's prediction of 80,353 ± 6 MeV from electroweak fits and directly contradicts the 2022 CDF measurement of 80,433.5 ± 9.4 MeV that had suggested the existence of new physics beyond the Standard Model [1].

"It's just a huge relief, to be honest," said Kenneth Long of MIT [1]. The CDF result, announced four years ago by the Fermilab collaboration, had deviated from theory by seven standard deviations — a result so statistically significant that hundreds of theoretical papers were written attempting to explain it. The CMS result, based on 117 million W → μν events collected in 2016 at 13 TeV, achieves similar precision to CDF but lands squarely where the Standard Model said it should.

The CMS Collaboration involves more than 3,000 members. Their measurement effectively closes a chapter that had generated enormous excitement in particle physics. If the CDF result had been confirmed, it would have been the first laboratory evidence that the Standard Model — the most successful theory in physics — was incomplete in a measurable, specific way.

Instead, physics' most reliable framework survives another test. The Standard Model remains unbroken, which is both a triumph of theoretical prediction and a disappointment for anyone hoping that new fundamental particles were finally within reach.