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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.
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.
The discovery finally convinced the physics community of the quark model's validity. [35] In the following years a number of suggestions appeared for extending the quark model to six quarks. Of these, the 1975 paper by Haim Harari [41] was the first to coin the terms top and bottom for the additional quarks. [42]
Pions, which are mesons with zero spin, are composed of first-generation quarks. In the quark model, an up quark and an anti-down quark make up a π +, whereas a down quark and an anti-up quark make up the π −, and these are the antiparticles of one another. The neutral pion π 0
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 ...
) which decays into a down quark (d) and a down antiquark (d). In particle physics, a kaon, also called a K meson and denoted K, [a] 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 ...