The Standard Model and beyond

The Standard Model is a theory that describes the how the basic building blocks of the universe fit together. It is the best theory physicists have to predict the properties and behaviors of particles at a subatomic scale.

Particles are classified into two groups: fermions and bosons.

Fermions—which are quarks and leptons—create the subatomic scaffolding for solid matter. Quarks bind together to create protons and neutrons; electrons orbit these clusters of quarks to form atoms; and atoms combine into all known stable matter in the universe.

Bosons, on the other hand, are the forces that allow matter to interact. The strong force—which is carried by a boson call a gluon—essentially “glues” clumps of quarks into protons and neutrons and then glues protons and neutrons into atomic nuclei.

The weak force—which is carried by the W and Z bosons—governs how atoms break apart (radioactive decay) and hadrons merge together (fusion). Without the weak force, protons could not fuse with neutrons, and therefore the sun could not shine, let alone exist.

The electromagnetic force—carried by the photon—draws electrons to atomic nuclei and binds atoms into molecules. It also allows light to travel and magnets to attract metals.

Despite its incredible success, the Standard Model still cannot explain key concepts in our understanding of the universe. For instance, why is there an imbalance of matter and antimatter in the universe? How does gravity fit into our model? Why can we observe the effect of dark matter in the cosmos, but we cannot see it in the lab? Why are there exactly three families of fundamental particles? Why is the mass scale of subatomic matter so imbalanced?

Physicists know that there must be new physics beyond the Standard Model that answers these lingering questions. And there are thousands of theories that endeavor to unite our current understanding of the universe with new ideas that fill in these gaps. But without experimental evidence to support or refute these theories, physicists are still in the dark.

US scientists and our international collaborators hope that research from the Large Hadron Collider will elucidate some of these mysteries of nature and bring us closer to a united theory of mass, matter and the universe.

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