Quark model in the context of "George Zweig"

In physics, the eightfold way is an organizational scheme for a class of subatomic particles known as hadrons that led to the development of the quark model. The American physicist Murray Gell-Mann and the Israeli physicist Yuval Ne'eman independently and simultaneously proposed the idea in 1961.The name comes from Gell-Mann's (1961) paper, "The Eightfold Way: A theory of strong interaction symmetry." It is an allusion to the Noble Eightfold Path of Buddhism and was meant to be a joke.

In particle physics, a kaon, also called a K meson and denoted K, is any of a group of four mesons distinguished by a quantum number called strangeness. In the quark model they are understood to be bound states of a strange quark (or antiquark) and an up or down antiquark (or quark).

In particle physics, a tetraquark is an exotic meson composed of four valence quarks. A tetraquark state has long been suspected to be allowed by quantum chromodynamics, the modern theory of strong interactions. A tetraquark state is an example of an exotic hadron that lies outside the conventional quark model classification. A number of different types of tetraquark have been observed.

In particle physics, exotic mesons are mesons that have quantum numbers not possible in the quark model; some proposals for non-standard quark model mesons could be:

All exotic mesons are classed as mesons because they are hadrons and carry zero baryon number. Of these, glueballs must be flavor singlets – that is, must have zero isospin, strangeness, charm, bottomness, and topness. Like all particle states, exotic mesons are specified by the quantum numbers which label representations of the Poincaré symmetry, q.e., by the mass (enclosed in parentheses), and by J, where J is the angular momentum, P is the intrinsic parity, and C is the charge conjugation parity; One also often specifies the isospin I of the meson. Typically, every quark model meson comes in SU(3) flavor nonet: an octet and an associated flavor singlet. A glueball shows up as an extra (supernumerary) particle outside the nonet.

A pentaquark is a subatomic particle, consisting of four quarks and one antiquark bound together. Evidence for the existence of pentaquarks has been found in decays of the Bottom lambda baryon.

As quarks have a baryon number of ⁠++1/3⁠, and antiquarks of ⁠−+1/3⁠, the pentaquark would have a total baryon number of 1, and thus would be a baryon. Further, because it has five quarks instead of the usual three found in regular baryons (a.k.a. "triquarks"), it is classified as an exotic baryon. The name pentaquark was coined by Claude Gignoux et al. (1987) and Harry J. Lipkin in 1987; however, the possibility of five-quark particles was identified as early as 1964 when Murray Gell-Mann first postulated the existence of quarks. Although predicted for decades, pentaquarks proved surprisingly difficult to discover and some physicists were beginning to suspect that an unknown law of nature prevented their production.

In high-energy physics, a pseudoscalar meson is a meson with total spin 0 and odd parity (usually notated as J = 0 ).Pseudoscalar mesons are commonly seen in proton–proton scattering and proton–antiproton annihilation, and include the pion (π), kaon (K), eta (η), and eta prime (η′) particles, whose masses are known with great precision.

Among all of the mesons known to exist, in some sense, the pseudoscalars are the most well studied and understood.

In high energy physics, a vector meson is a meson with total spin 1 and odd parity (usually noted as J = 1). Vector mesons have been seen in experiments since the 1960s, and are well known for their spectroscopic pattern of masses.

The vector mesons contrast with the pseudovector mesons, which also have a total spin 1 but instead have even parity. The vector and pseudovector mesons are also dissimilar in that the spectroscopy of vector mesons tends to show nearly pure states of constituent quark flavors, whereas pseudovector mesons and scalar mesons tend to be expressed as composites of mixed states.