Baryons

Abstract

Baryons are made of three quarks. The charge conjugated partners are the antibaryons which consist of the three corresponding antiquarks. However, candidates for pentaquark baryons made of four quarks and one antiquark have been reported (Sect. 16.3). Let us first deal with the ordinary ones made of qqq or $\overline {qqq}$. Baryons have the baryon number B = 1 and antibaryons B = −1. Those containing only light (u and d) quarks are called N for isospin i = $\frac {1}{2}$ and Δ for i = $\frac {3}{2}$ (the proton and neutron are usually abbreviated to p and n). Hyperons are baryons containing at least one s quark. Baryons with two light quarks are labelled Λ for i = 0 and Σ for i = 1. Those containing only one light quark are called Ξ and are isospin doublets. Those without any light quark are called Ω and are isospin singlets. The number of c or b quarks in a baryon is indicated by the subscripts c or b. The mass in MeV is specified in parentheses, except for the long-lived (“stable”) ones which decay through the weak interaction.