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A long-awaited calculation of the W boson's mass agrees with theory, contradicting a previous anomaly that had raised the possibility of new physics beyond the Standard Model Physicists have nailed a fiendishly difficult measurement — the mass of the fundamental particle the W boson. The result, from the CMS experiment at the Large Hadron Collider (LHC), is in line with the predictions of the standard model, and pours cold water on an anomaly in the W boson mass that surfaced in 2022. That measurement had hinted at the existence of phenomena beyond the standard model, physicists' best description of particles and forces.
"The standard model is not dead," said Josh Bendavid, a particle physicist at the Massachusetts Institute of Technology in Cambridge and member of the CMS collaboration, when he presented the result on 17 September. Rapturous applause met the announcement, made at a seminar at CERN, Europe's particle-physics laboratory near Geneva, Switzerland, which hosts the LHC. CMS's result was was 10 years in the making, and produced a mass of 80,360.
2 million electronvolts for the W boson, which is involved in carrying the weak nuclear force. If the finding had been close to the 2022 result, we would be declaring the standard model's death, said Bendavid. "The community will be excited by the fact that we can reach this precision and have this understanding of the standard model at this level," says Florencia Canelli, an experimental particle physicist at the University of Zurich in Switzerland, who works on the CMS experiment but was not involved in the result.
On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Relief for physicists The 2022 result, produced by an experiment called CDF at the Fermi National Accelerator Laboratory.
.. Elizabeth Gibney.
