Physicists have been studying the results of the Tevatron collider for 10 years and concluded that the experimental value of the W boson is seriously different from what the Standard Model gives. And so there is a possibility that we need to change physics as we know it.
What happened?
The W boson is a fundamental particle that carries a weak nuclear force. It turned out to be much heavier than according to the Standard Model of physics.
A difference of 0.09% was established between theoretical and experimental data. It seems small, but this error is much larger than the standard error of 0.01%.
This is incredibly important information for all physicists in the world, says Florence Canelli, a physicist at the University of Zurich. If the findings are confirmed in other experiments, it would be the first serious discrepancy with the Standard Model of physics – this theory, which describes all the particles that make up matter, and all the fundamental interactions, except gravity.
Yes, the Standard Model is not valid for all processes. So if at least one serious inconsistency appears, the model will have to be changed. But there are physicists who are cautious about the results of the experiment.
Generating a W-boson mass measurement based on experimental data is a very complicated process, I would be careful to interpret the existing discrepancy with the Standard Model, says Matthias Schott, a physicist at Johannes Gutenberg University. He believes physicists need to understand as accurately as possible why such discrepancies occurred.
What do we know about the W boson?
The particle was discovered in 1983. Experiments at the time calculated that the W boson weighs 85 protons. The error of this value was 5% or more, as it was difficult to calculate the mass.
The Z-boson and W-boson are involved in most nuclear reactions, particularly in fusion, which takes place on the Sun. W- and Z-bosons carry a weak nuclear force, one of the four fundamental forces of nature. The W boson is studied in colliders, where particles are produced and then pushed together at high energy. The particles can be detected as they decay into a subspecies of electrons, or into muons and neutrinos. The neutrino disappears without a trace, but the electron and muon can be tracked.
In the process of decay, most of the original mass of the W boson is converted into the energy of the new particles. If physicists can measure this energy, and determine how the particles decay, they can determine the mass of the W boson. But if it is impossible to trace the actions of the neutrino, it is also impossible to say exactly what part of the energy of the electron or muon is related to mass, and what part is related to momentum.
What did the authors of the new work do?
In an article published in the journal Science, the researchers report nearly a decade of analysis of data collected using the Tevatron particle gas pedal. These measurements, the authors say, are more accurate than all others combined. The authors calculated that the mass of the W boson is about 157 thousand times the mass of the electron. Thanks to the new measurement it is possible to check the relevance of the Standard Model of physics.
What is new physics?
This is the name given to physical laws that go beyond the Standard Model. And the new work, this is not the first hint of such physics. A similar situation occurred with the muon-g2 experiment in 2021. But the accuracy of that work was much lower than the new results.
The W-boson mass value was higher than expected by as much as seven standard deviations – meaning that the probability that it is a fluke is about one in a trillion.
“This measurement is the most significant deviation from the fundamental prediction of the Standard Model, more than scientists have ever recorded. So I think it’s a hint that we don’t yet fully understand the weak nuclear force or all the particles that experience that force,” said Ashutosh Kotwal, a professor at Duke University.
What will the new discovery change in physics?
The implications of this discovery have yet to be fully understood. One could simply adjust the Standard Model according to the new measurements. But the authors of the paper believe they are witnessing the beginning of a paradigm shift and the emergence of previously unknown physics.
An important first step along the way is to obtain independent confirmation. Now the 400 scientists who worked on the experiment are going together with other physicists to analyze the result in order to understand where to go next. The Large Hadron Collider at CERN is collecting data on the W boson, and new experiments could be conducted on it.
“If a new electron-positron collider is built, it will also be able to measure the mass of the W boson very accurately. In addition, the Large Hadron Collider and small specialized experiments measure new particles and their interactions very accurately. If there is new physics, it will be possible to observe it in these experiments,” Professor Kotwal explained.
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