Hadron

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In particle physics, a hadron is a composite subatomic particle made of two or more quarks that are held together by the strong nuclear force. Pronounced , the name is derived from Ancient Greek ἁδρός (hadrós) 'stout, thick'. They are analogous to molecules, which are held together by the electromagnetic force. Most of the mass of ordinary matter comes from two hadrons: the proton and the neutron, while most of the mass of the protons and neutrons is in turn due to the binding energy of their constituent quarks, due to the strong force. Hadrons are categorized into two broad families: baryons, made of an odd number of quarks (usually three), and mesons, made of an even number of quarks (usually two: one quark and one antiquark). Protons and neutrons (which make the majority of the mass of an atom) are examples of baryons; pions are an example of a meson. A tetraquark state (an exotic meson), named the Z(4430)−, was discovered in 2007 by the Belle Collaboration and confirmed as a resonance...

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