Quark

Quarks (pronounced: /kwɔrk/ or IPA: /kwɑrk/) are a type of elementary particle and are major constituents of matter. Quarks combine to form composite particles called hadrons, the best-known of which are protons and neutrons. They are the only particles in the Standard Model to experience the strong interaction in addition to the other three fundamental interactions, also known as fundamental forces. Due to a phenomenon known as color confinement, quarks are never in isolation; they can only be found within hadrons. For this reason, much of what is known about quarks has been drawn from observations of the hadrons themselves.

There are six different types of quarks, known as flavors: up (symbol: ), down (), charm (), strange (), top () and bottom (). 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. Because of this, the heavier charm, strange, top and bottom quarks can only be produced in high energy collisions, such as in particle accelerators and cosmic rays.

Quarks have various intrinsic properties, including electric charge, color charge, spin and mass. For every quark flavor there is a corresponding antiparticle, called antiquark, that differs from the quark only in that some of its properties have the opposite sign. Quarks are the only known elementary particles whose electric charge comes in fractions of the elementary charge.