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Jefferson Lab's Scientific Mission - What We Study

The Lab is pursuing three major research topics.

Structure of the Nucleus

In this simple view of a nucleus, quarks (red, blue and green) inside three nucleons are interacting by exchanging particles. Larger version.

The nucleus of the atom contains nearly all of the atom's mass. That's true of the atoms in all matter, whether they're in the car you drive to work or a neighbor's schnauzer. In the simplest of all atoms, hydrogen, the single proton in the nucleus is nearly 2000 times more massive than the electron zipping around the atom's perimeter.

Jefferson Lab scientists and users are studying the structure of nuclear matter; that is, how protons and neutrons (called nucleons) combine to make the nucleus and what forces bind nucleons together.

They are also peering deep inside the nucleus to uncover more elementary building blocks of matter. Nucleons are made of quarks and gluons. At Jefferson Lab, researchers are probing the nucleus to uncover at what distance and energy scale it ceases to appear to be made up of individual nucleons and instead appears to be made up of their constituent quarks and gluons.

Structure of Nucleons

Protons and neutrons are comprised of three valence quarks held together by the exchange of gluons, along with a quark-gluon sea of particles that are constantly popping into and out of existence. Jefferson Lab is researching how quarks, gluons and the quark-gluon sea combine to form nucleons and what forces mediate these interactions.

Jefferson Lab scientists and users are also studying how forces on the scale of quarks and gluons bind nucleons together. According to Quantum Chromodynamics (QCD), the fundamental theory of particle physics, quarks are bound together by the strong force. The force is carried by gluons in the form of a special charge called color, and quarks and gluons both have color. Color charge comes in three varieties: red, blue and green. Quarks can only exist in combinations where their color charges add up to "no color." For instance, a proton has a quark of each color, which add together to make the proton color neutral ("no color").

Researching how quarks are formed, how they combine to make other particles and what rules govern these interactions will help physicists understand the most fundamental particles and forces in nature.

Tests of the Standard Model

The Standard Model is a theory that describes fundamental particles and their interactions in terms of the strong, weak and electromagnetic forces. Scientists at Jefferson Lab are using CEBAF's accelerator to study the completeness of the Standard Model and the values of its free parameters. Probing the model's limits and discovering where it fails allows physicists to develop ever more accurate and inclusive theories of matter, giving them insights into the fundamental particles of nature.