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Definition: A quark is one of the fundamental particles in physics. They join together to form hadrons, such as protons and neutrons. The study of quarks and the interactions between them is called quantum chromodynamics.

The anti-particle of a quark is the antiquark. Quarks and antiquarks are the only two fundamental particles that interact through all four fundamental forces of physics.

A quark exhibits confinement, which means that the quarks are not observed independently but always in combination with other quarks. This makes determining the properties (mass, spin, and parity) impossible to measure directly; these traits must be inferred from the particles composed of them.

These measurements indicate a non-integer spin (either +1/2 or -1/2), so quarks are fermions and follow the Pauli Exclusion Principle. There are 6 flavours of quarks: up, down, strange, charm, bottom, and top.

The flavour of the quark determines its properties. Quarks with a charge of +(2/3)e are called up-type quarks and those with a charge of -(1/3)e are called down-type. There are three generations of quarks, based on pairs of weak positive/negative weak isospin. The first generation are up & down quarks, the second generation are strange & charm quarks, the third generation are top & bottom quarks.

All quarks have a baryon number (B = 1/3) and a lepton number (L = 0). The flavour determines certain other unique properties, described in individual descriptions. (See links to the right.)

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