The W boson appears more massive than previous measurements showed. What is the implication for the Standard Model of particle physics?
Four fundamental forces govern the Universe: the strong force, the weak force, the electromagnetic force and the gravitational force. The “W boson” is the mediator of the weak force (the W corresponds to weak, “weak” in English). This particle was discovered in the 1980s. Its mass has since been identified and refined. Except that a study, published in Science on April 7, 2022, carries the most precise measurement to date of the W boson, and we discover a much larger mass than previously calculated. Clearly: the W boson is heavier than expected.
This is unfortunate, because the Standard Model of particle physics relies on this measurement. However, this model is a real house of cards, and a larger mass than expected can topple a lot of things. In the case of the W boson, as a mediator of the weak interaction, it is notably at the heart of a process such as nuclear fusion – at the heart of stars. A whole part of our conception of the Universe is therefore linked to the correct measurement of the W boson.
450 trillion collisions (more or less)
One could postulate a miscalculation. It is not impossible in this kind of case. The problem is the immense precision of the measurement: it involved 400 scientists for 10 years on a data set of around 450,000 billion collisions at Fermilab (these collisions come from the old particle accelerator Tevatron , since closed).
” Numerous collider experiments have produced measurements of the mass of the W boson over the past 40 years “, details, in a commentary on the study, the physicist Giorgio Chiarelli. ” These are difficult and complicated measurements, and they have achieved ever greater precision. It took us many years to work out all the details and carry out the necessary checks. This is our most robust measurement to date, and the discrepancy between measured and expected values persists. »
This mass difference between what is predicted and what is measured is now a mystery, which will have to be resolved. It will be necessary at the same time to reconfirm the measurement – even if it turns out to be the most precise today – and then to find a tangible explanation for it within the standard model of the Universe.
” 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, chances are it’s something that can be discovered during future experiences explains David Toback, one of the authors.
