Editing Hadron (section)

==Mesons==
{{Main|Meson|Exotic meson}}
[[Meson]]s are hadrons containing an even number of valence quarks (at least two).<ref name=GellMann-1964/> Most well known mesons are composed of a quark-antiquark pair, but possible [[tetraquark]]s (four quarks) and [[hexaquark]]s (six quarks, comprising either a dibaryon or three quark-antiquark pairs) may have been discovered and are being investigated to confirm their nature.<ref name=Mann-2013-06-Wired/> Several other hypothetical types of [[exotic meson]] may exist which do not fall within the quark model of classification. These include [[glueball]]s and [[hybrid meson]]s (mesons bound by excited [[gluon]]s).

Because mesons have an even number of quarks, they are also all [[boson]]s, with integer [[Spin (physics)|spin]], ''i.e.'', 0, +1, or −1. They have baryon number {{nobr|{{math| ''B'' {{=}} {{sfrac|1|3}} − {{sfrac|1|3}} {{=}} 0 }}.}} Examples of mesons commonly produced in particle physics experiments include [[pion]]s and [[kaon]]s. Pions also play a role in holding [[atomic nuclei]] together via the [[residual strong force]].