On April 7, this year, in a paper in Science, researchers from Collider Detector at Fermi lab (CDF) Collaboration analyzed ten years of data and announced that they have made a precise detection of the mass of the so-called W boson and that it does not match with the value expected from estimates using the standard model and previous measurements. If confirmed by other experiments, this would be a sign of the incompleteness, or even incorrectness, of the Standard Model of particle physics.r All newsletter explains all things Science, without the jargon.
The U.S. Department of Energy has formally approved the start of full construction for the PIP-II project, an essential upgrade to the accelerator complex at Fermi National Accelerator Laboratory. The heart of the project is a powerful new superconducting linear accelerator that will enable the world’s most intense high-energy neutrino beam.
The milestone, known as Critical Decision 3, authorizes the project to begin full-scale procurement and construction. It builds on the March 2021 approval for a preliminary construction start, which enabled work on key elements needing longer preparation times. This included cutting-edge technologies such as superconducting and high-power radio frequency systems and instrumentation.
“We are elated to have reached this crucial step for PIP-II,” said LIA Merminga, Fermi lab director and former PIP-II project director. “Our team around the world has worked tirelessly to prepare for this moment. The planning has paid off, and we are excited to move into the construction phase, knowing it will make incredible new science possible.”
The W boson is an elementary particle that plays an important role in mediating weak nuclear interactions. The weak nuclear force is one of the four fundamental interactions between matter particles in physics, the others being electromagnetic interaction, strong nuclear interaction, and gravitational interactions. In quantum electrodynamics, the theory that describes electromagnetic interactions, the photon is the particle that mediates the interaction – for example, charged particles exchange a photon when they interact. In the case of weak interactions, there are three such ‘gauge bosons’ – the W+ (W-plus), W- (W-minus), and Z particles. Unlike the photon, the W-plus and W-minus are charged, and by exchanging such bosons, a neutron can change into a proton, for example. This helps in the transmutation of elements. The W boson helps the interactions that make the Sunburn and produce energy.
Inspired by the success of quantum electrodynamics, Sheldon Glasgow, Abdul Salem, and Steven Weinberg developed the similar but more general ‘electroweak’ theory in which they predicted these three particles and how they mediated the weak interactions. They were given the Nobel Prize for their efforts in 1979. The W boson was first discovered at CERN, located on the Franco-Swiss border. Unlike the photon, which is massless, the W bosons are quite massive, which results in the force they mandate – the weak force – being very short-ranged.
The Standard Model of particle physics has been very successful in predicting the behavior of elementary particles, for about 60 years now, since its inception. It predicted the existence of the Higgs boson which was discovered, also at CERN, in 2012. However, there are glaring gaps – the SM does not describe gravity, and has no room to include dark matter particles. The latest discovery, that the W boson mass is not agreeing with the value allowed by the standard model, would be another crack in the theory. This finding by Fermi lab awaits being confirmed by other major experiments.
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