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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.
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.
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]
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 ...
, negatively charged (containing a strange quark and an up antiquark) has mass 493.677 ± 0.013 MeV and mean lifetime (1.2380 ± 0.0020) × 10 −8 s. K + ( antiparticle of above) positively charged (containing an up quark and a strange antiquark ) must (by CPT invariance ) have mass and lifetime equal to that of
Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged pions π + and π − decaying after a mean lifetime of 26.033 nanoseconds (2.6033 × 10 −8 seconds), and the neutral pion π 0
The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime. The combination of a bottom antiquark and a bottom quark is not a B meson, but rather bottomonium, which is something else entirely. Each B meson has an antiparticle that is composed of a bottom quark and an up (B − ...