Hadrons

In particle physics, a hadron ⁱ/ˈhædrɒn/ (Greek: ἁδρός, hadrós, "stout, thick") is a composite particle made of quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force.

Hadrons are categorized into two families: baryons, made of three quarks, and mesons, made of one quark and one antiquark. Protons and neutrons are examples of baryons; pions are an example of a meson. Hadrons containing more than three valence quarks (exotic hadrons) have been discovered in recent years. A tetraquark state (an exotic meson), named the Z(4430)⁻, was discovered in 2007 by the Belle Collaboration and confirmed as a resonance in 2014 by the LHCb collaboration. Two pentaquark states (exotic baryons), named P+
c(4380) and P+
c(4450), were discovered in 2015 by the LHCb collaboration. There are several more exotic hadron candidates, and other colour-singlet quark combinations may also exist.

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