Since mesons are composed of quarks, they participate in both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction. They are classified according to their quark content, total angular momentum, parity, and various other properties such as C-parity and G-parity. While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and will exhibit higher-energy phenomena sooner than baryons would. For example, the charm quark was first seen in the J/Psi meson ( J/ψ ) in 1974,[1][2] and the bottom quark in the upsilon meson ( ϒ ) in 1977.[3] The top quark (the last and heaviest quark to be discovered to date) was first observed at Fermilab in 1995.
Each meson has a corresponding antiparticle (antimeson) where quarks are replaced by their corresponding antiquarks and vice versa. For example, a positive pion ( π+ ) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion ( π− ), is made of one up antiquark and one down quark. Although tetraquarks with two quarks and two antiquarks can be considered mesons they are not listed here.
Because this table was initially derived from published results and many of those results were preliminary, as many as 64 of the mesons in the following table may not exist or have the wrong mass or quantum numbers.
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 IG of 1+ and 0− respectively.[5]
The, "f", "a", "b" and "h" mesons are not listed in the tables below and their internal structure and quark content is a matter of ongoing investigation.[6][7]
The particle described in the table above as f0(500) has historically been known by two other names: f0(600) and σ (sigma).[8]
A complete set of meson naming conventions is set forth in a 2017 review article for the Particle Data Group which also contains a table mapping pre-2016 common names to the new Particle Data Group standard naming conventions for XYZ mesons.[9]
Meson properties
The following lists details for all known and predicted pseudoscalar (JP = 0−) and vector (JP = 1−) mesons.
The properties and quark content of the particles are tabulated below; for the corresponding antiparticles, simply change quarks into antiquarks (and vice versa) and flip the sign of Q, B, S, C, and B′. Particles with † next to their names have been predicted by the standard model but not yet observed. Values in red have not been firmly established by experiments, but are predicted by the quark model and are consistent with the measurements.
[a]^ Makeup inexact due to non-zero quark masses. [b]^ PDG reports the resonance width (Γ). Here the conversion τ = ħ⁄Γ is given instead. [c]^Strongeigenstate. No definite lifetime (see kaon notes below) [d]^ The mass of the K0 L and K0 S are given as that of the K0 . However, it is known that a difference between the masses of the K0 L and K0 S on the order of 2.2×10−11 MeV/c2 exists.[19] [e]^Weakeigenstate. Makeup is missing small CP–violating term (see notes on neutral kaons below).
[f]^ PDG reports the resonance width (Γ). Here the conversion τ = ħ⁄Γ is given instead. [g]^ The exact value depends on the method used. See the given reference for detail.
Note that these issues also exist in principle for other neutral flavored mesons; however, the weak eigenstates are considered separate particles only for kaons because of their dramatically different lifetimes.[38]
^Kan Chen, et al., "Light axial vector mesons" Phys. Rev. D 91, 074025 (2015) doi: 10.1103/PhysRevD.91.074025 open access copy available at https://arxiv.org/abs/1501.07766
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van Beveren, Eef; Rupp, George (5–10 June 2006). Scalar and axial-vector mesons. IVth International Conference on Quarks and Nuclear Physics (QNP06) (plenary talk) (with subsequent corrections ed.). Madrid, ES. arXiv:hep-ph/0610199.
^
Pelaez, J.R. (2016). "From controversy to precision on the sigma meson: A review on the status of the non-ordinary resonance". Physics Reports. 658: 1–111. arXiv:1510.00653. Bibcode:2016PhR...658....1P. doi:10.1016/j.physrep.2016.09.001. S2CID118569293. The existence and properties of the sigma meson have been controversial for almost six decades, despite playing a central role in the spontaneous chiral symmetry of QCD or in the nucleon–nucleon attraction. This controversy has also been fed by the strong indications that it is not an ordinary quark–antiquark meson.
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Patrignani, C.; et al. (Particle Data Group) (2016). "Revised naming-scheme for hadrons". Chin. Phys. C. 40: 100001.
"2017 update"(PDF).