Organization Group representation theory is the mathematical underpinning behind the eightfold way but this rather technical mathematics is not needed to understand how it helps organize particles. Particles are sorted into groups as mesons or baryons. Within each group, they are further separated by their spin angular momentum. Symmetrical patterns appear when these groups of particles have their strangeness plotted against their electric charge. (This is the most common way to make these plots today but originally physicists used an equivalent pair of properties called hypercharge and isotopic spin, the latter of which is now known as isospin.) The symmetry in these patterns is a hint of the underlying symmetry of the strong interaction between the particles themselves. In the plots below, points representing particles that lie along the same horizontal line share the same strangeness, , while those on the same left-leaning diagonals share the same electric charge, (given as multiples of the elementary charge). Mesons In the original eightfold way, the mesons were organized into octets and singlets. This is one of the finer points of differences between the eightfold way and the quark model it inspired, which suggests the mesons should be grouped into nonets (groups of nine). Meson octet The eightfold way organizes eight of the lowest spin-0 mesons into an octet. They are: , , and kaons , , and pions Diametrically opposite particles in the diagram are anti-particles of one-another while particles in the center are their own anti-particle. Meson singlet The chargeless, strangeless eta prime meson was originally classified by itself as a singlet: Under the quark model later developed, it is better viewed as part of a meson nonet, as previously mentioned. Baryons Baryon octet The eightfold way organizes the spin- baryons into an octet. They consist of neutron (n) and proton (p) , , and sigma baryons , the strange lambda baryon and xi baryons Baryon decuplet The organizational principles of the eightfold way also apply to the spin- baryons, forming a decuplet. , , , and delta baryons , , and sigma baryons and xi baryons omega baryon However, one of the particles of this decuplet had never been previously observed when the eightfold way was proposed. Gell-Mann called this particle the and predicted in 1962 that it would have a strangeness −3, electric charge −1 and a mass near . In 1964, a particle closely matching these predictions was