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Mesons are made of a valence quark–antiquark pair (thus have a baryon number of 0), while baryons are made of three quarks (thus have a baryon number of 1). This article discusses the quark model for the up, down, and strange flavors of quark (which form an approximate flavor SU(3) symmetry). There are generalizations to larger number of flavors.
Because mesons are composed of quark subparticles, they have a meaningful physical size, a diameter of roughly one femtometre (10 −15 m), [1] which is about 0.6 times the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few tenths of a nanosecond.
Mesons named with the letter "f" are scalar mesons (as opposed to a pseudo-scalar meson), and mesons named with the letter "a" are axial-vector mesons (as opposed to an ordinary vector meson) a.k.a. an isoscalar vector meson, while the letters "b" and "h" refer to axial-vector mesons with positive parity, negative C-parity, and quantum numbers I G of 1 + and 0 − respectively.
The quark composition of the ω meson can be thought of as a mix between u u, d d and s s states, but it is very nearly a pure symmetric u u-d d state. This can be shown by deconstructing the wave function of the ω into its component parts. We see that the ω and ϕ mesons are mixtures of the SU(3) wave functions as follows. [7]
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. Both the American physicist Murray Gell-Mann and the Israeli physicist Yuval Ne'eman independently and simultaneously proposed the idea in 1961.
Ordinary mesons are made up of a valence quark and a valence antiquark. Because mesons have integer spin (0 or 1) and are not themselves elementary particles, they are classified as "composite" bosons, although being made of elementary fermions. Examples of mesons include the pion, kaon, and the J/ψ.
particles belong to the "pseudo-scalar" nonet of mesons which have spin J = 0 and negative parity, [9] [10] and η and η′ have zero total isospin, I, and zero strangeness, and hypercharge. Each quark which appears in an η particle is accompanied by its antiquark, hence all the main quantum numbers are zero, and the particle overall is ...
The Standard Model of particle physics is the theory ... This interaction is mediated by mesons, ... Quantum chromodynamics, Quark model; Weak interaction ...