Physicists discover A fundamental particle called the W boson appears to be 0.1 percent heavier—a tiny difference that could herald a huge shift in fundamental physics.
Measurements reported in the journal April 7 science, an old-fashioned particle collider from Fermi National Accelerator Laboratory in Batavia, Illinois, which smashed its last proton a decade ago. About 400 members of Fermilab’s (CDF) collaborating collider detector continue to analyze the W bosons produced by the collider known as the Tevatron, tracking countless sources of error to an unrivaled level of precision.
If W’s excess relative to standard theory predictions can be independently verified, the discovery would suggest the existence of an undiscovered particle or force, and would lead to the first major rewrite of the laws of quantum physics in half a century.
“This will revolutionize the way we see the world,” which may even rival the discovery of the Higgs boson in 2012, said Sven Heinemeyer, a physicist at the Institute of Theoretical Physics in Madrid. , he is not part of the CDF. “The Higgs particle fits very well with what was known before. This will be a whole new field.”
The discovery comes at a time when the physics community is hungry for flaws in the Standard Model of particle physics, the long-ruled system of equations that captures all known particles and forces. The Standard Model is known to be incomplete, and there are many unsolved mysteries, such as the nature of dark matter. The strong track record of CDF collaboration makes their new results a credible threat to the Standard Model.
“They produced hundreds of beautiful measurements,” said theoretical physicist Aida El-Khadra of the University of Illinois at Urbana-Champaign. “They are known to be careful.”
But no one has opened the champagne yet. While the new mass measurement of W alone is quite different from the predictions of the Standard Model, other experiments weighing W have produced results that are less dramatic (albeit less precise). For example, in 2017, the ATLAS experiment at Europe’s Large Hadron Collider measured the mass of the W particle and found it to be only a little heavier than the Standard Model says. The conflict between CDF and ATLAS suggests that one or both groups overlooked some subtle quirks of their experiments.
“I want it to be confirmed and to understand the difference from previous measurements,” said Guillaume Unal, a physicist at CERN and a member of the ATLAS experiment in the laboratory where the Large Hadron Collider is located. “The W bosons must be the same on both sides of the Atlantic.”
“It’s a landmark work,” said MIT Nobel Prize-winning physicist Frank Wilczek, “but it’s hard to know what to do with it.”
The W boson, along with the Z boson, regulates the weak force, one of the four fundamental forces of the universe. Unlike gravity, electromagnetism, and the strong force, the weak force doesn’t push or pull too much, but instead converts heavier particles into lighter ones. For example, a muon will spontaneously decay into a W boson and a neutrino, and then the W becomes an electron and another neutrino. The associated subatomic deformations cause radioactivity and help keep sunlight out.
Over the past 40 years, various experiments have measured the mass of the W and Z bosons. The mass of the W boson has proven to be a particularly tantalizing target. While other particle masses must simply be measured and accepted as a fact of nature, the W mass can be predicted by incorporating a handful of other measurable quantum properties in the Standard Model equations.