Quarks

Quarks are matter particles which constitute neutrons and protons. They are the only particles in to experience all four fundamental forces, which are also known as fundamental interactions. There are six different types of quarks. Each quark type is called a flavor. Single quarks are not usually found on their own. They can only be found in composite particles called hadrons, such as protons and neutrons. Thus much of what we know about quarks has been inferred from observations on the hadrons themselves.

As they are confined by the strong force fields, quarks only exist inside hadrons. As a result, it is impossible measure their mass by isolating them. There are six types of quarks which are known as flavors: up (u), down (d), charm (c), strange (s), top (t) and bottom (b). The up and down quarks have the lowest masses of all quarks, and thus are generally stable and very common in the universe. The other quarks are much more massive, and will rapidly decay into the lighter up and down quarks. The heavier charm, strange, top and bottom quarks can only be produced in high energy collisions, such as in particle accelerators and cosmic rays.