What is the Standard Model of Particle Physics?

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The standard model includes particles of matter (quarks and leptons), force-carrying particles (bosons) and the Higgs boson. Credit: Illustration courtesy of Sandbox Studio, Chicago for Symmetry

The Standard Model of particle physics is scientists’ current best theory for describing the most basic building blocks of the universe. It explains how particles called quarks (which make up protons and neutrons) and leptons (which include electrons) make up all known matter. It also explains how force-carrying particles, which belong to a larger group of bosons, influence quarks and leptons.

The Standard Model explains three of the four fundamental forces that govern the universe: electromagnetism, the strong force and the weak force. Electromagnetism is carried by photons and involves the interaction of electric fields and magnetic fields. The strong force, which is carried by the gluons, binds the atomic nuclei to make them stable. The weak force, carried by the W and Z bosons, causes nuclear reactions that have powered our Sun and other stars for billions of years. The fourth fundamental force is gravity, which is not sufficiently explained by the standard model.

Despite its success in explaining the universe, the Standard Model has limitations. For example, the Higgs boson gives mass to quarks, charged leptons (like electrons), and W and Z bosons. However, we don’t yet know if the Higgs boson also gives mass to neutrinos – ghostly particles that very rarely interact with other matter in the universe. Additionally, physicists understand that approximately 95% of the universe is not made of ordinary matter as we know it. Instead, much of the universe is made up of dark matter and dark energy that doesn’t fit the Standard Model.

DOE Office of Science: Contributions to the Standard Model of Particle Physics

The DOE has a long history of supporting fundamental particle research. Five of the six types of quarks, one type of lepton, and all three neutrinos were discovered at what are now DOE National Laboratories. Researchers supported by the DOE Office of Science, often in collaboration with scientists around the world, contributed to the Nobel Prize-winning discoveries and measurements that refined the Standard Model. These efforts continue today, with experiments performing precision tests of the Standard Model and further improving measurements of particle properties and their interactions. Theorists work with experimental scientists to develop new ways to explore the Standard Model. This research may also provide insight into the kinds of particles and unknown forces that could explain dark matter and dark energy, as well as what happened to antimatter after the big bang.

Standard Model of Particle Physics Facts

  • Any ordinary matter, including any atom on the periodic table of elements, consists of only three types of matter particles: up and down quarks, which make up the protons and neutrons in the nucleus, and the electrons which surround the nucleus.
  • The complete standard model took a long time to build. Physicist JJ Thomson discovered the electron in 1897, and Large Hadron Collider scientists found the final piece of the puzzle, the Higgs boson, in 2012.

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