But the excitement in the physics community is tempered with a loud note of caution. Although the Fermilab result is the most accurate measurement of the mass of the W boson to date, it is at odds with two of the next most accurate measurements from two separate experiments which are in line with the Standard Model.
"This will ruffle some feathers", says Prof Ben Allanach, a theoretical physicist at Cambridge University.
"We need to know what is going on with the measurement. The fact that we have two other experiments that agree with each other and the Standard Model and strongly disagree with this experiment is worrying to me".
Jan Stark, physicist and director of research at the French CNRS institute, said "this is either a major discovery or a problem in the analysis of data," predicting "quite heated discussions in the years to come".
He told AFP that "extraordinary claims require extraordinary evidence".
Although the difference between the theoretical prediction and experimental value is only 0.09%, it is significantly larger than the result’s error margins, which are less than 0.01%. The finding also disagrees with some other measurements of the mass. The collaboration that ran the latest experiment, called CDF at the Fermi National Accelerator Laboratory (Fermilab), reported the findings in Science1 on 7 April.
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Some physicists strike a note of caution. Generating a W boson mass measurement from experimental data is famously complex. Although the work is impressive, “I would be cautious to interpret the significant difference to the standard model as a sign of new physics,” says Matthias Schott, a physicist at the Johannes Gutenberg University Mainz in Germany, who works on the ATLAS experiment at CERN, Europe’s particle-physics lab near Geneva, Switzerland. Physicists should prioritize working out why the value differs from the other recent results, he says.
