2023-04-20 16:00:00
2012 was the last big year for particle physics. It was the year that those responsible for CERN announced the discovery of the Higgs bosonthat is, the particle that gave mass to all the others and that ended up completing the hitherto unfinished standard model of particle physics. The finding earned physicists Peter Higgs y Francois Englert, although 5 decades after having predicted the particle, the Nobel Prize in Physics in 2013.
Since then it can be said that not much has happened in the field of particle physics. Or at least until now, because if the discovery of the Higgs boson came to make sense of a model that physicists from all over the world had been trying to fit since 1970, a new discovery made by scientists from the Fermilab Collision Detector -CDF – and the US Department of Energy’s Fermi National Laboratory could have arrived to dismantle many of the foundations on which the Standard Model rests.
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A very accurate measurement
What they have just announced, 10 years later, is neither more nor less than the most accurate measurement to date of the mass of another of the 6 bosons that make up the standard model: the W boson. There is only one problem, and that is that, as reflected in the article that includes the finding, published on April 7 in the journal Science Under the title High-precision measurement of the W boson mass with the CDF II detector, the measurements do not correspond to what was predicted by the model. It’s like being told that an element on the periodic table shouldn’t be where it is.
According to the new measurement, the mass of the W boson is significantly higher than predicted by theory, with a standard deviation of 7 sigma.
Thus, scientists have now determined the mass of the particle with an accuracy of 0.01%, two times better than the best previous measurement. The result is that, surprisingly, the researchers found that the mass of the W boson was significantly higher than predicted by theory, with a standard deviation of 7 sigma, which means that the new measurement is far from the mean of previously obtained measurements for the particle.
The surprisingly high value for the mass of the W boson is a dart straight to the fundamental heart at the heart of the Standard Model, the theoretical framework that describes nature at its most fundamental level, and in which both in the experimental field and in theoretical predictions the parameters were firmly established and well established.
“The CDF measurement was done over many years, when we discovered the value, it was a surprise,” says CDF physicist Chris Hays of the University of Oxford. “We were counting on our understanding of our particle accelerator better than ever after so many years, and we took into account the latest advances in theoretical and experimental understanding of the W boson’s interactions with other particles. When we finally revealed the result, we found that it differed from the standard model prediction,” continues Ashutosh V. Kotwal, the Duke University physicist who led the test and one of the 400 CFD scientists who participated in the study. But while this is an intriguing result, the measurement must be confirmed by new experiments before it can be fully considered valid,” adds Fermilab deputy director Joe Lykken.
What is the W boson and what does this new measurement change?
A boson is one of the two basic types of elementary particles of nature (the other type are fermions). There are 6 types, of which four of them, among which is found in the W boson, make up what are known as Gauge bosons; the fifth would be the previously named Higgs boson, and the last one, the so-called graviton, which until now has not been discovered, so for the moment it is relegated to the theoretical field.
W bosons mediate the weak interaction, which together with the strong nuclear force, gravity and the electromagnetic force is one of the fundamental forces of physics and nature. It is responsible for the nuclear processes that make the sun shine and particles decay.
Photo: Fabsanhvasq / Cc
The mass of a W boson is about 80 times the mass of a proton, approximately 80,000 MeV/c2. For more than 20 years, CDF researchers have worked to achieve increasingly precise measurements of the mass of the W boson. The results of this experiment, which used the entire data set collected from the Tevatron collider at Fermilab, are was based on the observation of 4.2 million W boson candidates. But as explained by Giorgio Chiarelli, from the Italian National Institute for Nuclear Physics (INFN-Pisa) and co-spokesperson for the CDF, “although it has taken the team many years to review all the details, carry out the necessary controls and it is our most robust measurement to date, there are still discrepancies between the measured and expected values”.
Also co-spokesman for CDF and professor of physics and astronomy at Texas A&M University, David Toback, says for his part that the result is an important contribution to testing the accuracy of the Standard Model. “It is now up to the community of theoretical physics to carry out new experiments and follow up on the results to shed light on this new mystery in physics,” he continues, as If this measure is confirmed, it is possible that rethinking or improving the model on which our understanding of nature is based. “If the difference between the experimental value and the expected value is due to some kind of new particle or subatomic interaction, which is one of the possibilities, it is very likely that we will discover new interesting things in the future,” he says.
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