Baryons are strongly interacting fermions; that is, they are acted on by the strong nuclear force and are described by Fermi−Dirac statistics, which apply to all particles obeying the Pauli exclusion principle. This is in contrast to the bosons, which do not obey the exclusion principle.
Baryons, along with mesons, are hadrons, particles composed of quarks. Quarks have baryon numbers of B = 1/3 and antiquarks have baryon numbers of B = −1/3. The term "baryon" usually refers to triquarks—baryons made of three quarks (B = 1/3 + 1/3 + 1/3 = 1).
Other exotic baryons have been proposed, such as pentaquarks—baryons made of four quarks and one antiquark (B = 1/3 + 1/3 + 1/3 + 1/3 − 1/3 = 1), but their existence is not generally accepted. The particle physics community as a whole did not view their existence as likely in 2006, and in 2008, considered evidence to be overwhelmingly against the existence of the reported pentaquarks. However, in July 2015, the LHCb experiment observed two resonances consistent with pentaquark states in the Λ0
b → J/ψK−
p decay, with a combined statistical significance of 15σ.
In theory, heptaquarks (5 quarks, 2 antiquarks), nonaquarks (6 quarks, 3 antiquarks), etc. could also exist.