Editing Eightfold way (physics) (section)

==Organization==
[[Group representation theory]] is the mathematical underpinning of the eightfold way, but that 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 (physics)|spin]] angular momentum. Symmetrical patterns appear when these groups of particles have their [[Strangeness (particle physics)|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, {{mvar|s}}, while those on the same left-leaning diagonals share the same electric charge, {{mvar|q}} (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====
[[Image:meson octet.png|thumb|The [[pseudoscalar meson]] octet]]
The eightfold way organizes eight of the lowest [[Spin (physics)|spin]]-0 [[meson]]s into an octet.<ref name=Gell-Mann-1961-TID-12608/><ref name=Gell-Mann-1962/> They are:
* {{SubatomicParticle|Kaon0}}, {{SubatomicParticle|Kaon+}}, {{SubatomicParticle|Kaon-}} and {{SubatomicParticle|AntiKaon0}} [[kaon]]s
* {{SubatomicParticle|pion+}}, {{SubatomicParticle|pion0}}, and {{SubatomicParticle|pion-}} [[pion]]s
* {{SubatomicParticle|eta}}, the [[eta meson]]

Diametrically opposite particles in the diagram are [[anti-particle]]s 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:
* [[Eta meson|{{SubatomicParticle|eta prime}}]]

Under the quark model later developed, it is better viewed as part of a meson nonet, as previously mentioned.

===Baryons===

====Baryon octet====
[[Image:Baryon octet.png|thumb|The {{mvar|J}} = {{sfrac|1|2}} [[baryon]] octet]]
The eightfold way organizes the [[Spin (physics)|spin]]-{{sfrac|1| 2 }} [[baryon]]s into an octet. They consist of
* [[neutron]] (n) and [[proton]] (p) 
* {{SubatomicParticle|sigma-}}, {{SubatomicParticle|sigma0}}, and {{SubatomicParticle|sigma+}} [[sigma baryon]]s
* {{Subatomic particle|Lambda0}}, the [[lambda baryon|strange lambda baryon]]
* {{SubatomicParticle|xi-}} and {{SubatomicParticle|xi0}} [[xi baryon]]s

====Baryon decuplet====
[[Image:Baryon decuplet.png|thumb|The {{mvar|J}} = {{sfrac|3|2}} [[baryon decuplet]]]]
The [[Special unitary group#Lie algebra 3|organizational principles of the eightfold way]] also apply to the spin-{{sfrac|3|2}} baryons, forming a [[Baryon#Isospin and charge|decuplet]].
* {{SubatomicParticle|delta-}}, {{SubatomicParticle|delta0}}, {{SubatomicParticle|delta+}}, and {{SubatomicParticle|delta++}} [[delta baryon]]s
* {{SubatomicParticle|sigma*-}}, {{SubatomicParticle|sigma*0}}, and {{SubatomicParticle|sigma*+}} [[sigma baryon]]s
* {{SubatomicParticle|xi*-}} and {{SubatomicParticle|xi*0}} [[xi baryon]]s
* {{SubatomicParticle|omega-}} [[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 {{SubatomicParticle|link=yes|Omega-}} and predicted in 1962 that it would have a [[strangeness]] &minus;3, [[electric charge]] &minus;1 and a mass near {{val|1680|u=MeV/c2}}. In 1964, a particle closely matching these predictions was discovered<ref name=Barnes-Connolly-etal-1964/> by a [[particle accelerator]] group at [[Brookhaven National Laboratory|Brookhaven]]. Gell-Mann received the 1969 [[Nobel Prize in Physics]] for his work on the theory of [[elementary particle]]s.