Editing Meson

{{Short description|Subatomic particle; made of equal numbers of quarks and antiquarks}}
{{About|the subatomic particle|the software|Meson (software)}}
{{Infobox Particle
| name = Mesons
| image = [[File:Meson nonet - spin 0.svg|200px]]
| caption = Mesons of spin 0 form a [[wikt:nonet|nonet]]
| num_types = ~140 ([[List of mesons|List]])
| composition = [[Composite particle|composite]]: [[quark]]s and [[antiparticle|antiquark]]s
| statistics = [[boson]]ic
| group = [[hadron]]
| generation =
| interaction = [[Strong interaction|strong]], [[Weak interaction|weak]], [[Electromagnetic interaction|electromagnetic]] and [[gravity]]
| particle =
| antiparticle =
| status =
| theorized = [[Hideki Yukawa]] (1935)
| discovered = 1947
| symbol =
| mass = from 134.9&nbsp;MeV/''c''<sup>2</sup> ({{#invoke:particles|link|pion0}})<br/>to 9.460&nbsp;GeV/''c''<sup>2</sup> ({{#invoke:particles|link|Upsilon}})
| decay_time =
| decay_particle =
| electric_charge = −1&nbsp;[[elementary charge|''e'']], 0&nbsp;''e'', +1&nbsp;''e''
| color_charge =
| spin = 0&nbsp;[[reduced Planck constant|''ħ'']], 1&nbsp;''ħ''
| num_spin_states =
}}
{{Standard model of particle physics}}

In [[particle physics]], a '''meson''' ({{IPAc-en|ˈ|m|iː|z|ɒ|n|,_|ˈ|m|ɛ|z|ɒ|n}}) is a type of [[hadron]]ic [[subatomic particle]] composed of an equal number of [[quark]]s and [[antiquark]]s, usually one of each, bound together by the [[strong interaction]]. Because mesons are composed of quark subparticles, they have a meaningful physical size, a diameter of roughly one [[femtometre]] (10{{sup|−15}}&nbsp;m),<ref name="D. Griffiths (2008)">{{cite book |last1=Griffiths |first1=D. |year=2008 |title=Introduction to Elementary Particles |edition=2nd |publisher=Wiley-VCH |isbn=978-3-527-40601-2 }}</ref> which is about 0.6&nbsp;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.  Heavier mesons decay to lighter mesons and ultimately to stable [[electron]]s, [[neutrino]]s and [[photon]]s.

Outside the nucleus, mesons appear in nature only as short-lived products of very high-energy collisions between particles made of quarks, such as [[cosmic ray]]s (high-energy protons and neutrons) and [[baryonic matter]]. Mesons are routinely produced artificially in [[cyclotron]]s or other [[particle accelerator]]s in the collisions of protons, [[antiproton]]s, or other particles.

Higher-energy (more massive) mesons were created momentarily in the [[Big Bang]], but are not thought to play a role in nature today. However, such heavy mesons are regularly created in particle accelerator experiments that explore the nature of the heavier quarks that compose the heavier mesons.

Mesons are part of the [[hadron]] particle family, which are defined simply as particles composed of two or more quarks. The other members of the hadron family are the [[baryon]]s: subatomic particles composed of odd numbers of valence quarks (at least three), and some experiments show evidence of [[exotic meson]]s, which do not have the conventional valence quark content of two quarks (one quark and one antiquark), but four or more.

Because quarks have a spin {{sfrac|1|2}}, the difference in quark number between mesons and baryons results in conventional two-quark mesons being [[boson]]s, whereas baryons are [[fermion]]s.

Each type of meson has a corresponding [[antiparticle]] (antimeson) in which quarks are replaced by their corresponding antiquarks and vice versa. For example, a positive [[pion]] ({{SubatomicParticle|Pion+}}) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion ({{SubatomicParticle|Pion-}}), is made of one up antiquark and one down quark.

Because mesons are composed of quarks, they participate in both the [[weak interaction]] and [[strong interaction]]. Mesons with net [[electric charge]] also participate in the [[electromagnetic interaction]]. Mesons are classified according to their quark content, [[total angular momentum]], [[parity (physics)|parity]] and various other properties, such as [[C-parity]] and [[G-parity]]. Although no meson is stable, those of lower [[mass]] are nonetheless more stable than the more massive, and hence are easier to observe and study in [[particle accelerator]]s or in [[cosmic ray]] experiments. The lightest group of mesons is less massive than the lightest group of baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher-energy phenomena more readily than do baryons. But mesons can be quite massive: for example, the [[J/ψ meson|J/Psi meson]] ({{SubatomicParticle|J/Psi}}) containing the [[charm quark]], first seen 1974,<ref name="J.J. Aubert ''et al.'' (1974)"/><ref name="J.E. Augustin ''et al.'' (1974)"/> is about three times as massive as a proton, and the [[upsilon meson]] ({{SubatomicParticle|Upsilon}}) containing the [[bottom quark]], first seen in 1977,<ref name="S.W. Herb ''et al.'' (1977)"/> is about ten times as massive as a proton.

== History ==
From theoretical considerations, in 1934 [[Hideki Yukawa]]<ref>{{cite web |publisher=The Noble Foundation |year=1949 |title=Nobel Prize in Physics 1949 |series=Presentation Speech |url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1949/press.html}}</ref><ref name="H. Yukawa, (1935)">{{cite journal |last=Yukawa |first=H. |year=1935 |title=On the Interaction of Elementary Particles |journal=Proc. Phys.-Math. Soc. Jpn. |volume=17 |issue=48  |url=http://web.ihep.su/dbserv/compas/src/yukawa35/eng.pdf}}</ref> predicted the existence and the approximate mass of the "meson" as the carrier of the [[nuclear force]] that holds [[atomic nucleus|atomic nuclei]] together.<ref>{{cite journal |first=Hideki |last=Yukawa |year=1935 |title=On the Interaction of Elementary Particles. I |journal=Nippon Sugaku-Buturigakkwai Kizi Dai 3 Ki |volume=17 |pages=48–57 |doi=10.11429/ppmsj1919.17.0_48 |publisher=日本物理学会、日本数学会 |url=https://www.jstage.jst.go.jp/article/ppmsj1919/17/0/17_0_48/_pdf/-char/en}}</ref> If there were no nuclear force, all nuclei with two or more [[proton]]s would fly apart due to [[Electromagnetism|electromagnetic]] repulsion. [[Hideki Yukawa|Yukawa]] called his carrier particle the meson, from μέσος ''mesos'', the [[Ancient Greek|Greek]] word for "intermediate", because its predicted mass was between that of the electron and that of the proton, which has about 1,836&nbsp;times the mass of the electron. [[Hideki Yukawa|Yukawa]] or [[Carl David Anderson]], who discovered the [[muon]], had originally named the particle the "mesotron", but he was corrected by the physicist [[Werner Heisenberg]] (whose father was a professor of Greek at the [[University of Munich]]). Heisenberg pointed out that there is no "tr" in the Greek word "mesos".<ref name="G. Gamow, (1961)">{{cite book |last1=Gamow |first1=G. |orig-year=1961 |title=The Great Physicists from Galileo to Einstein |publisher=Dover Publications |year=1988 |isbn=978-0-486-25767-9 |edition=Reprint |url=https://archive.org/details/greatphysicistsf0000gamo |url-access=registration |page=[https://archive.org/details/greatphysicistsf0000gamo/page/315 315] }}</ref>

The first candidate for Yukawa's meson, in modern terminology known as the [[muon]], was discovered in 1936 by [[Carl David Anderson]] and others in the [[decay product]]s of cosmic ray interactions. The [[muon|"mu meson"]] had about the right mass to be Yukawa's carrier of the strong nuclear force, but over the course of the next decade, it became evident that it was not the right particle. It was eventually found that the [[muon|"mu meson"]] did not participate in the strong nuclear interaction at all, but rather behaved like a heavy version of the [[electron]], and was eventually classed as a [[lepton]] like the electron, rather than a meson. Physicists in making this choice decided that properties other than particle mass should control their classification.

There were years of delays in the subatomic particle research during [[World War II]] (1939–1945), with most physicists working in applied projects for wartime necessities. When the war ended in August&nbsp;1945, many physicists gradually returned to peacetime research. The first true meson to be discovered was what would later be called the [[pion|"pi meson"]] (or pion). During 1939–1942, [[Debendra Mohan Bose]] and [[Bibha Chowdhuri]] exposed [[Ilford Photo|Ilford]] [[half-tone]] photographic plates in the high altitude mountainous regions of [[Darjeeling]], and observed long curved ionizing tracks that appeared to be different from the tracks of alpha particles or protons. In a series of articles published in ''[[Nature (journal)|Nature]]'', they identified a cosmic particle having an average mass close to 200 times the mass of electron.<ref name="science_and_culture_76">
{{cite journal
 | title = D. M. Bose: A Scientist Incognito (editorial)
 | volume = 76
 | issue = 11–12
 | journal = Science and Culture
 | date=November–December 2010
 | url = http://www.scienceandculture-isna.org/Nov-Dec-10/Editorial.pdf
 | access-date = 5 February 2011
}}</ref> This discovery was made in 1947 with improved full-tone photographic emulsion plates, by [[Cecil Powell]], [[Hugh Muirhead]], [[César Lattes]], and [[Giuseppe Occhialini]], who were investigating cosmic ray products at the [[University of Bristol]] in [[England]], based on photographic films placed in the Andes mountains.<ref>{{cite journal |author1=Lattes, C. |author2=Occhialini, G. |author3=Muirhead, H. |author4=Powell, C. |year=1947 |title=Processes involving charged mesons |journal=[[Nature (journal)|Nature]] |volume=159 |pages=694–698 |doi=10.1007/s00016-014-0128-6|s2cid=122718292 }}</ref> Some of those mesons had about the same mass as the already-known mu "meson", yet seemed to decay into it, leading physicist [[Robert Marshak]] to hypothesize in 1947 that it was actually a new and different meson. Over the next few years, more experiments showed that the pion was indeed involved in strong interactions. The pion (as a [[virtual particle]]) is also used as force carrier to model the [[nuclear force]] in [[atomic nucleus|atomic nuclei]] (between [[proton|protons]] and [[neutron|neutrons]]). This is an approximation, as the actual carrier of the strong force is believed to be the [[gluon]], which is explicitly used to model strong interaction between quarks. Other mesons, such as the virtual [[rho meson]]s are used to model this force as well, but to a lesser extent. Following the discovery of the pion, Yukawa was awarded the 1949 [[Nobel Prize in Physics]] for his predictions.

For a while in the past, the word ''meson'' was sometimes used to mean ''any'' force carrier, such as [[W and Z bosons|"the Z{{sup|0}} meson"]], which is involved in mediating the [[weak interaction]].<ref name ="J. Steinberger, (1998)">{{cite journal |last1=Steinberger |first1=J. |year=1989 |title=Experiments with high-energy neutrino beams |url=https://cds.cern.ch/record/193654 |journal=[[Reviews of Modern Physics]] |volume=61 |issue=3 |pages=533–545 |bibcode = 1989RvMP...61..533S |doi=10.1103/RevModPhys.61.533 |pmid=17747881 }}</ref> However, this use has fallen out of favor, and mesons are now defined as particles composed of pairs of quarks and antiquarks.

== Overview ==

=== Spin, orbital angular momentum, and total angular momentum ===
{{Main|Spin (physics)|angular momentum operator|Total angular momentum|Quantum numbers}}
[[Spin (physics)|Spin]] (quantum number {{mvar|S}}) is a [[Euclidean vector|vector]] quantity that represents the "intrinsic" [[angular momentum]] of a particle. It comes in increments of {{sfrac|1|2}}&nbsp;[[Planck constant|{{mvar|ħ}}]].{{efn|
group=upper-alpha|
The {{mvar|ħ}} is often dropped because it is the "fundamental" unit of spin, and it is implied that "spin&nbsp;1" means "spin 1&nbsp;{{mvar|ħ}}". In some systems of [[natural units]], {{mvar|ħ}} is chosen to be 1, and therefore drops out of equations. The remainder of this article uses the "assume {{mvar|ħ}} units" convention for all types of spin.
}}

[[Quark]]s are [[fermion]]s—specifically in this case, particles having spin {{sfrac|1|2}} {{nobr|( {{mvar|S}} {{=}} {{sfrac|1|2}} ).}} Because spin projections vary in increments of 1 (that is 1&nbsp;{{mvar|ħ}}), a single quark has a spin vector of length {{sfrac|1|2}}, and has two spin projections, either {{nobr|( {{mvar|S}}{{sub|z}} {{=}} +{{sfrac|1|2}} }} or {{nobr| {{mvar|S}}{{sub|z}} {{=}} {{sfrac|&minus;|1|2}} ).}} Two quarks can have their spins aligned, in which case the two spin vectors add to make a vector of length {{nobr| {{mvar|S}} {{=}} 1 ,}} with three possible spin projections {{nobr|( {{mvar|S}}{{sub|z}} {{=}} +1,}} {{nobr| {{mvar|S}}{{sub|z}} {{=}} 0,}} and {{nobr| {{mvar|S}}{{sub|z}} {{=}} −1),}} and their combination is called a ''[[vector meson]]'' or [[Vector boson|spin-1]] triplet. If two quarks have oppositely aligned spins, the spin vectors add up to make a vector of length {{nobr| {{mvar|S}} {{=}} 0,}} and only one spin projection {{nobr|( {{mvar|S}}{{sub|z}} {{=}} 0 ),}} called a ''[[scalar meson]]'' or [[Scalar boson|spin-0]] singlet. Because mesons are made of one quark and one antiquark, they are found in triplet and singlet spin states. The latter are called [[scalar meson]]s or [[pseudoscalar meson]]s, depending on their parity (see below).

There is another quantity of quantized [[angular momentum]], called the [[angular momentum operator#Orbital angular momentum|orbital angular momentum]] (quantum number {{mvar|L}}), that is the angular momentum due to quarks orbiting each other, and also comes in increments of 1&nbsp;{{mvar|ħ}}. The total angular momentum (quantum number {{mvar|J}}) of a particle is the combination of the two intrinsic angular momentums (spin) and the orbital angular momentum. It can take any value from {{nobr| {{mvar|J}} {{=}} {{!}}{{mvar|L}} − {{mvar|S}}{{!}} }} up to {{nobr| {{mvar|J}} {{=}} {{!}}{{mvar|L}} + {{mvar|S}}{{!}} ,}} in increments of 1.

{|class="wikitable" style="margin-left:auto; margin-right:auto; text-align:center;"
|+ Meson angular momentum quantum numbers for {{mvar|L}} = 0, 1, 2, 3
|-
! style="width:30px;"| [[Spin (physics)|{{mvar|S}}]]
! style="width:30px;"| [[Angular momentum operator#Orbital angular momentum|{{mvar|L}}]]
! style="width:30px;"| [[#Parity|{{math|P}}]]
! style="width:50px;"| [[Total angular momentum|{{mvar|J}}]]
! style="width:70px;"| {{mvar|J}}{{sup|{{math|P}}}}
|-
|rowspan="4"| 0
| 0 || − || 0 || 0{{sup|−}}
|-
| 1 || + || 1 || 1{{sup|+}}
|-
| 2 || − || 2 || 2{{sup|−}}
|-
| 3 || + || 3 || 3{{sup|+}}
|-
|rowspan="4"| 1
| 0 || − || 1 || 1{{sup|−}}
|-
| 1 || + || 2,<!-- 1, --> 0 || 2{{sup|+}},<!-- 1{{sup|+}}, --> 0{{sup|+}}
|-
| 2 || − || 3,<!-- 2, --> 1 || 3{{sup|−}},<!-- 2{{sup|−}}, --> 1{{sup|−}}
|-
| 3 || + || 4,<!-- 3, --> 2 || 4{{sup|+}},<!-- 3{{sup|+}}, --> 2{{sup|+}}
|}

Particle physicists are most interested in mesons with no orbital angular momentum ({{mvar|L}}&nbsp;=&nbsp;0), therefore the two groups of mesons most studied are the {{mvar|S}}&nbsp;=&nbsp;1; {{mvar|L}}&nbsp;=&nbsp;0 and {{mvar|S}}&nbsp;=&nbsp;0; {{mvar|L}}&nbsp;=&nbsp;0, which corresponds to {{mvar|J}}&nbsp;=&nbsp;1 and {{mvar|J}}&nbsp;=&nbsp;0, although they are not the only ones. It is also possible to obtain {{mvar|J}}&nbsp;=&nbsp;1 particles from {{mvar|S}}&nbsp;=&nbsp;0 and {{mvar|L}}&nbsp;=&nbsp;1. How to distinguish between the {{mvar|S}}&nbsp;=&nbsp;1, {{mvar|L}}&nbsp;=&nbsp;0 and {{mvar|S}}&nbsp;=&nbsp;0, {{mvar|L}}&nbsp;=&nbsp;1 mesons is an active area of research in [[meson spectroscopy]].<ref>{{cite web |title=Particles of the Standard Model |url=https://pdfslide.net/documents/particles-of-the-standard-model.html |website=pdfslide.net |language=en |access-date=2020-05-24 |df=dmy-all}}</ref>

=== {{math|P}}-parity ===
{{Main|Parity (physics)}}
{{math|P}}-parity is left-right parity, or spatial parity, and was the first of several "parities" discovered, and so is often called just [[Parity (physics)|"parity"]]. If the universe were reflected in a mirror, most laws of physics would be identical—things would behave the same way regardless of what we call "left" and what we call "right". This concept of mirror reflection is called [[parity (physics)|parity]] ({{math|P}}). [[Gravity]], the [[electromagnetic force]], and the [[strong interaction]] all behave in the same way regardless of whether or not the universe is reflected in a mirror, and thus are said to [[P-symmetry|conserve parity]] ({{math|P}}-symmetry). However, the [[weak interaction]] does'' ''distinguish "left" from "right", a phenomenon called [[parity violation]] ({{math|P}}-violation).

Based on this, one might think that, if the [[wavefunction]] for each particle (more precisely, the [[quantum field]] for each particle type) were simultaneously mirror-reversed, then the new set of wavefunctions would perfectly satisfy the laws of physics (apart from the weak interaction). It turns out that this is not quite true: In order for the equations to be satisfied, the wavefunctions of certain types of particles have to be multiplied by −1, in addition to being mirror-reversed. Such particle types are said to have ''negative'' or ''odd'' parity ({{math|P}}&nbsp;=&nbsp;−1, or alternatively {{math|P}}&nbsp;=&nbsp;&minus;), whereas the other particles are said to have ''positive'' or ''even'' parity ({{math|P}}&nbsp;=&nbsp;+1, or alternatively {{math|P}}&nbsp;=&nbsp;+).

For mesons, parity is related to the orbital angular momentum by the relation:<ref name=PDGQuarkmodel>
{{cite web
 |first1=C. |last1=Amsler
 |display-authors=etal
 |collaboration=[[Particle Data Group]]
 |year=2008
 |title=Quark Model
 |series=Reviews
 |publisher=[[Lawrence Berkeley Laboratory]]
 |url=http://pdg.lbl.gov/2008/reviews/quarkmodrpp.pdf
}}
</ref><ref name=Amsler-etal-PDG-2008/>

: <math>P = \left( -1 \right)^{L + 1}</math>
where the {{mvar|L}} is a result of the parity of the corresponding [[spherical harmonic]] of the [[wavefunction]]. The "+1" comes from the fact that, according to the [[Dirac equation]], a quark and an antiquark have opposite intrinsic parities. Therefore, the intrinsic parity of a meson is the product of the intrinsic parities of the quark (+1) and antiquark (−1). As these are different, their product is −1, and so it contributes the "+1" that appears in the exponent.

As a consequence, all mesons with no orbital angular momentum ({{mvar|L}}&nbsp;=&nbsp;0) have odd parity ({{math|P}}&nbsp;=&nbsp;−1).

=== C-parity ===
{{Main|C-parity}}
{{math|C}}-parity is only defined for mesons that are their own antiparticle (i.e. neutral mesons). It represents whether or not the wavefunction of the meson remains the same under the interchange of their quark with their antiquark.<ref name="M.S. Sozzi (2008b)">{{cite book |last1=Sozzi |first1=M. S. |year=2008b |chapter=Charge Conjugation |title=Discrete Symmetries and CP Violation: From Experiment to Theory |url=https://archive.org/details/discretesymmetri00msoz |url-access=limited |publisher=Oxford University Press |isbn=978-0-19-929666-8 |pages=[https://archive.org/details/discretesymmetri00msoz/page/n104 88]–120 }}</ref> If
: <math>|q\bar{q}\rangle = |\bar{q}q\rangle</math>
then, the meson is "{{math|C}} even" ({{math|C}}&nbsp;=&nbsp;+1). On the other hand, if
: <math>|q\bar{q}\rangle = -|\bar{q}q\rangle</math>

then the meson is "{{math|C}} odd" ({{math|C}}&nbsp;=&nbsp;−1).

{{math|C}}-parity rarely is studied on its own, but more commonly in combination with P-parity into [[CP-parity]]. {{math|CP}}-parity was originally thought to be conserved, but was later found to be violated on rare occasions in [[weak interaction]]s.<ref name="J.W. Cronin (1980)">{{cite web |last1=Cronin |first1=J.W. |year=1980 |title=CP Symmetry Violation—The Search for its origin |url=http://nobelprize.org/nobel_prizes/physics/laureates/1980/cronin-lecture.pdf |publisher=The Nobel Foundation }}</ref><ref name="V.L. Fitch (1980)">{{cite web |last1=Fitch |first=V.L. |year=1980 |title=The Discovery of Charge—Conjugation Parity Asymmetry |url=http://nobelprize.org/nobel_prizes/physics/laureates/1980/fitch-lecture.pdf |publisher=The Nobel Foundation }}</ref><ref name="M.S. Sozzi (2008c)">{{cite book |last1=Sozzi |first1=M. S. |year=2008c |chapter=CP-Symmetry |title=Discrete Symmetries and CP Violation: From Experiment to Theory |url=https://archive.org/details/discretesymmetri00msoz |url-access=limited |publisher=Oxford University Press |isbn=978-0-19-929666-8 |pages=[https://archive.org/details/discretesymmetri00msoz/page/n247 231]–275 }}</ref>

=== {{math|G}}-parity ===
{{Main|G-parity}}
{{math|G}}-parity is a generalization of the {{math|C}}-parity. Instead of simply comparing the wavefunction after exchanging quarks and antiquarks, it compares the wavefunction after exchanging the meson for the corresponding antimeson, regardless of quark content.<ref name="K. Gottfried, V.F. Weisskopf (1986)">{{cite book |last1=Gottfried |first1=K. |last2=Weisskopf |first2=V.F. |year=1986 |chapter=Hadronic spectroscopy: G-parity |title=Concepts of Particle Physics |url=https://archive.org/details/conceptsofpartic01kurt |url-access=limited |publisher=Oxford University Press |isbn=0-19-503393-0 |volume=2 |pages=[https://archive.org/details/conceptsofpartic01kurt/page/n137 303]–311 }}</ref>

If
: <math>|q_1\bar{q}_2\rangle = |\bar{q}_1 q_2\rangle</math>
then, the meson is "{{math|G}} even" ({{math|G}}&nbsp;=&nbsp;+1). On the other hand, if
: <math>|q_1\bar{q}_2\rangle = -|\bar{q}_1 q_2\rangle</math>
then the meson is "{{math|G}} odd" ({{math|G}}&nbsp;=&nbsp;−1).

=== Isospin and charge ===
{{Main|Isospin}}
{{anchor|Isospin_breaking}}
[[File:Meson nonet - spin 0.svg|thumb|200px| Combinations of one {{math|u}}, {{math|d}}, or {{math|s}} quark and one {{math|u}}, {{math|d}}, or {{math|s}} antiquark in {{nowrap| {{mvar|J}}{{sup|P}} {{=}} 0{{sup|−}} }} configuration form a [[wikt:nonet|nonet]].]]
[[File:Meson nonet - spin 1.svg|thumb|200px| Combinations of one {{math|u}}, {{math|d}}, or {{math|s}} quark and one {{math|u}}, {{math|d}}, or {{math|s}} antiquark in {{nowrap| {{mvar|J}}<sup>P</sup> {{=}} 1{{sup|−}} }} configuration also form a nonet.]]

==== Original isospin model ====
The concept of isospin was first proposed by [[Werner Heisenberg]] in 1932 to explain the similarities between protons and neutrons under the [[strong interaction]].<ref name="Heisenberg (1932)">
{{cite journal
 |last=Heisenberg |first=W. |author-link=Werner Heisenberg
 |year=1932
 |title=Über den Bau der Atomkerne
 |journal=[[Zeitschrift für Physik]]
 |volume=77 |issue=1–2 |pages=1–11
 |doi=10.1007/BF01342433
 |bibcode = 1932ZPhy...77....1H
 |s2cid=186218053
 |language=de
}}</ref> Although they had different electric charges, their masses were so similar that physicists believed that they were actually the same particle. The different electric charges were explained as being the result of some unknown excitation similar to spin. This unknown excitation was later dubbed ''isospin'' by [[Eugene Wigner]] in 1937.<ref name="Wigner (1937)">{{cite journal |last1=Wigner |first1=E. |year=1937 |title=On the Consequences of the Symmetry of the Nuclear Hamiltonian on the Spectroscopy of Nuclei |journal=[[Physical Review]] |volume=51 |issue=2 |pages=106–119 |bibcode=1937PhRv...51..106W |doi=10.1103/PhysRev.51.106 }}</ref>

When the first mesons were discovered, they too were seen through the eyes of isospin and so the three pions were believed to be the same particle, but in different isospin states.

The mathematics of isospin was modeled after the mathematics of [[Spin (physics)|spin]]. Isospin projections varied in increments of 1 just like those of spin, and to each projection was associated a "[[Quantum state|charged state]]". Because the "pion particle" had three "charged states", it was said to be of isospin {{nowrap| {{mvar|I}} {{=}} 1 .}} Its "charged states" {{SubatomicParticle|Pion+}}, {{SubatomicParticle|Pion0}}, and {{SubatomicParticle|Pion-}}, corresponded to the isospin projections {{nowrap| {{mvar|I}}{{sub|3}} {{=}} +1 ,}} {{nowrap| {{mvar|I}}{{sub|3}} {{=}} 0 ,}} and {{nowrap| {{mvar|I}}{{sub|3}} {{=}} −1 }} respectively. Another example is the "[[rho meson|rho particle]]", also with three charged states. Its "charged states" {{SubatomicParticle|rho+}}, {{SubatomicParticle|rho0}}, and {{SubatomicParticle|rho-}}, corresponded to the isospin projections {{nowrap| {{mvar|I}}{{sub|3}} {{=}} +1 ,}} {{nowrap| {{mvar|I}}{{sub|3}} {{=}} 0 ,}} and {{nowrap| {{mvar|I}}{{sub|3}} {{=}} −1 }} respectively.

==== Replacement by the quark model ====
This belief lasted until [[Murray Gell-Mann]] proposed the [[quark model]] in 1964 (containing originally only the {{math|u}}, {{math|d}}, and {{math|s}} quarks).<ref name="Gell-Mann (1964)">{{cite journal |last1=Gell-Mann |first1=M. |year=1964 |title=A Schematic of Baryons and Mesons |journal=[[Physics Letters]] |volume=8 |issue=3 |pages=214–215 |bibcode = 1964PhL.....8..214G |doi=10.1016/S0031-9163(64)92001-3 }}</ref> The success of the isospin model is now understood to be an artifact of the similar masses of the {{math|u}} and {{math|d}} quarks. Because the {{math|u}} and {{math|d}} quarks have similar masses, particles made of the same number of them also have similar masses.

The exact {{math|u}} and {{math|d}} quark composition determines the charge, because {{math|u}} quarks carry charge {{sfrac|+|2|3}} whereas {{math|d}} quarks carry charge {{sfrac|&minus;|1|3}}. For example, the three pions all have different charges
* {{math|{{SubatomicParticle|Pion+}} {{=}} ( {{SubatomicParticle|up quark}} {{SubatomicParticle|down antiquark}} ) }}
* {{math| {{SubatomicParticle|Pion0}}}} = a [[quantum superposition]] of {{math|( {{SubatomicParticle|up quark}} {{SubatomicParticle|up antiquark}}}} ) and {{math|( {{SubatomicParticle|down quark}} {{SubatomicParticle|down antiquark}} ) }} states 
* {{math|{{SubatomicParticle|Pion-}} {{=}} ( {{SubatomicParticle|down quark}} {{SubatomicParticle|up antiquark}} ) }}
but they all have similar masses ({{circa}} {{val|140|u=MeV/c2}}) as they are each composed of a same total number of up and down quarks and antiquarks. Under the isospin model, they were considered a single particle in different charged states.

After the [[quark model]] was adopted, physicists noted that the isospin projections were related to the up and down quark content of particles by the relation
: <math>I_3 = \frac{1}{2}\left[\left(n_\text{u} - n_\bar{\text{u}}\right) - \left(n_\text{d} - n_\bar{\text{d}}\right)\right],</math>
where the {{mvar|n}}-symbols are the count of up and down quarks and antiquarks.

In the "isospin picture", the three pions and three rhos were thought to be the different states of two particles. However, in the quark model, the rhos are excited states of pions. Isospin, although conveying an inaccurate picture of things, is still used to classify hadrons, leading to unnatural and often confusing nomenclature.

Because mesons are hadrons, the isospin classification is also used for them all, with the quantum number calculated by adding {{nowrap| {{mvar|I}}{{sub|3}} {{=}} +{{sfrac|1|2}} }} for each positively charged up-or-down quark-or-antiquark (up quarks and down antiquarks), and {{nowrap| {{mvar|I}}{{sub|3}} {{=}} &minus;{{sfrac|1|2}} }} for each negatively charged up-or-down quark-or-antiquark (up antiquarks and down quarks).

=== Flavour quantum numbers ===
{{Main|Flavour (particle physics)#Flavour quantum numbers}}
The [[strangeness]] [[Flavour quantum numbers|quantum number]] ''S'' (not to be confused with spin) was noticed to go up and down along with particle mass. The higher the mass, the lower (more negative) the strangeness (the more s quarks). Particles could be described with isospin projections (related to charge) and strangeness (mass) (see the uds nonet figures). As other quarks were discovered, new quantum numbers were made to have similar description of udc and udb nonets. Because only the u and d mass are similar, this description of particle mass and charge in terms of isospin and flavour quantum numbers only works well for the nonets made of one u, one d and one other quark and breaks down for the other nonets (for example ucb nonet). If the quarks all had the same mass, their behaviour would be called ''symmetric'', because they would all behave in exactly the same way with respect to the strong interaction. However, as quarks do not have the same mass, they do not interact in the same way (exactly like an electron placed in an electric field will accelerate more than a proton placed in the same field because of its lighter mass), and the symmetry is said to be [[broken symmetry|broken]].

It was noted that charge (''Q'') was related to the isospin projection (''I''<sub>3</sub>), the [[baryon number]] (''B'') and flavour quantum numbers (''S'', ''C'', ''{{prime|B}}'', ''T'') by the [[Gell-Mann–Nishijima formula]]:<ref name="S.S.M Wong (1998)">{{cite book |last1=Wong |first1=S.S.M. |year=1998 |chapter=Nucleon Structure |title=Introductory Nuclear Physics |publisher=John Wiley & Sons |isbn=0-471-23973-9 |edition=2nd |location=New York |pages=21–56 }}</ref>
: <math>Q = I_3 + \frac{1}{2}(B + S + C + B^\prime + T),</math>
where ''S'', ''C'', ''{{prime|B}}'', and ''T'' represent the [[strangeness]], [[charm (quantum number)|charm]], [[bottomness]] and [[topness]] flavour quantum numbers respectively. They are related to the number of strange, charm, bottom, and top quarks and antiquark according to the relations:
: <math>\begin{align}
         S &= -(n_\text{s} - n_\bar{\text{s}}) \\
         C &= +(n_\text{c} - n_\bar{\text{c}}) \\
  B^\prime &= -(n_\text{b} - n_\bar{\text{b}}) \\
         T &= +(n_\text{t} - n_\bar{\text{t}}),
\end{align}</math>
meaning that the Gell-Mann–Nishijima formula is equivalent to the expression of charge in terms of quark content:
: <math>Q=\frac{2}{3}[(n_\text{u}-n_\bar{\text{u}})+(n_\text{c}-n_\bar{\text{c}})+(n_\text{t}-n_\bar{\text{t}})]-\frac{1}{3}[(n_\text{d}-n_\bar{\text{d}})+(n_\text{s}-n_\bar{\text{s}})+(n_\text{b}-n_\bar{\text{b}})].</math>

== Classification ==
{{see also|List of mesons}}
Mesons are classified into groups according to their [[isospin]] (''I''), [[total angular momentum]] (''J''), [[parity (physics)|parity]] (''P''), [[G-parity]] (''G'') or [[C-parity]] (''C'') when applicable, and [[quark]] (q) content. The rules for classification are defined by the [[Particle Data Group]], and are rather convoluted.<ref name=PDGMesonsymbols>
{{cite web
 |first1=C. |last1=Amsler
 |display-authors=etal
 |collaboration=[[Particle Data Group]]
 |year=2008
 |title=Naming scheme for hadrons
 |series=Reviews
 |publisher=[[Lawrence Berkeley Laboratory]]
 |url=http://pdg.lbl.gov/2008/reviews/namingrpp.pdf 
}}</ref> The rules are presented below, in table form for simplicity.

=== Types of meson ===

Mesons are classified into types according to their spin configurations. Some specific configurations are given special names based on the mathematical properties of their spin configuration.

{| class="wikitable" style="margin:auto; text-align:center;margin:1em auto;"
|+Types of mesons<ref name="Burcham & Jobes (1995)">{{cite book |last1=Burcham |first1=W. E. |last2=Jobes |first2=M. |year=1995 |title=Nuclear and Particle Physics |publisher=Longman Publishing |isbn=0-582-45088-8 |edition=2nd }}</ref>
|-
! style="width:150px;"| Type
! style="width:60px;"| [[Spin (physics)|{{mvar|S}}]]
! style="width:60px;"| [[Angular momentum operator#Orbital angular momentum|{{mvar|L}}]]
! style="width:60px;"| [[Parity (physics)|{{mvar|P}}]]
! style="width:60px;"| [[Total angular momentum|{{mvar|J}}]]
! style="width:60px;"| {{mvar|J}}<sup>P</sup>
|-
| [[Pseudoscalar meson]] || 0 || 0 || − || 0 || 0{{sup|−}}
|-
| [[Pseudovector meson]] || 0, 1 || 1 || + || 1 || 1{{sup|+}}
|-
| [[Vector meson]] || 1 || 0, 2 || − || 1 || 1{{sup|−}}
|-
| [[Scalar meson]] || 1 || 1 || + || 0 || 0{{sup|+}}
|-
| [[Tensor meson]] || 1 || 1, 3 || + || 2 || 2{{sup|+}}
|}

=== Nomenclature ===

==== Flavourless mesons ====
Flavourless mesons are mesons made of pair of quark and antiquarks of the same flavour (all their [[flavour quantum number]]s are zero: [[Strangeness|{{mvar|S}}]] = 0, [[Charm (quantum number)|{{mvar|C}}]] = 0, [[Bottomness|{{mvar|{{prime|B}}}}]] = 0, [[Topness|{{mvar|T}}]]  = 0).{{efn|group=lower-roman|For the purpose of nomenclature, the isospin projection {{mvar|I}}{{sub|3}} is treated as if it were ''not'' a flavour quantum number. This means that the charged pion-like mesons ({{mvar|π}}{{sup|±}}, {{mvar|a}}{{sup|±}}, {{mvar|b}}{{sup|±}}, and {{mvar|ρ}}{{sup|±}} mesons) follow the rules of flavourless mesons, even if they aren't truly "flavourless".}} The rules for flavourless mesons are:<ref name=PDGMesonsymbols/>
{|class="wikitable" style="text-align:center;margin:1em auto;"
|+ Nomenclature of flavourless mesons
|-
! rowspan=2 | {{SubatomicParticle|quark}}{{SubatomicParticle|antiquark}} content
! rowspan=2 |  [[Isospin|{{mvar|I}}]] 
! colspan=4 | [[Total angular momentum|{{mvar|J}}]]{{sup|[[Parity (physics)|{{math|P}}]][[C-parity|{{math|C}}]]&nbsp;{{efn|group=lower-roman|name=Cparity| [[C-parity]] is only relevant for neutral mesons.}} }}
|-
! 0<sup>−+</sup>, 2<sup>−+</sup>, 4<sup>−+</sup>, ...
! 1<sup>+−</sup>, 3<sup>+−</sup>, 5<sup>+−</sup>, ...
! 1<sup>−−</sup>, 2<sup>−−</sup>, 3<sup>−−</sup>, ...
! 0<sup>++</sup>, 1<sup>++</sup>, 2<sup>++</sup>, ...
|-
|{{SubatomicParticle|up quark}}{{SubatomicParticle|down antiquark}}<br/><math>\mathrm{\tfrac{u\bar{u} - d\bar{d}}{\sqrt{2}}}</math><br/>{{SubatomicParticle|down quark}}{{SubatomicParticle|up antiquark}} || 1 || {{SubatomicParticle|link=yes|pion+}}<br/>{{SubatomicParticle|link=yes|pion0}}<br/>{{SubatomicParticle|link=yes|pion-}} || b<sup>+</sup><br/>b<sup>0</sup><br>b<sup>−</sup> || {{SubatomicParticle|link=yes|rho+}}<br>{{SubatomicParticle|link=yes|rho0}}<br/>{{SubatomicParticle|link=yes|rho-}} || a<sup>+</sup><br/>a<sup>0</sup><br/>a<sup>−</sup>
|-
|Mix of <br/>{{SubatomicParticle|up quark}}{{SubatomicParticle|up antiquark}}, {{SubatomicParticle|down quark}}{{SubatomicParticle|down antiquark}}, {{SubatomicParticle|strange quark}}{{SubatomicParticle|strange antiquark}} || 0 || {{SubatomicParticle|link=yes|Eta}}<br>{{SubatomicParticle|link=yes|Eta prime}} || h<br/>{{prime|h}} || {{SubatomicParticle|link=yes|omega meson}}<br/>{{SubatomicParticle|link=yes|phi meson}} || f<br/>{{prime|f}}
|-
|{{SubatomicParticle|Charm quark}}{{SubatomicParticle|Charm antiquark}} || 0 || {{SubatomicParticle|link=yes|Charmed Eta}} || h<sub>c</sub> || ψ{{efn|group=lower-roman|name=JPsi| For the special case {{mvar|J}}{{sup|{{math|PC}}}}{{=}}1{{sup|−−}}, the ψ is called the {{SubatomicParticle|link=yes|J/Psi}} }} || χ<sub>c</sub>
|-
|{{SubatomicParticle|Bottom quark}}{{SubatomicParticle|Bottom antiquark}} || 0 || {{SubatomicParticle|link=yes|Bottom Eta}} || h<sub>b</sub> || {{SubatomicParticle|link=yes|Upsilon}} || χ<sub>b</sub>
|-
|{{SubatomicParticle|Top quark}}{{SubatomicParticle|Top antiquark}} || 0 || {{SubatomicParticle|link=yes|Top Eta}} || h<sub>t</sub> || {{SubatomicParticle|link=yes|Theta meson}} || χ<sub>t</sub>
|}

{{reflist|group=lower-roman}}

;In addition:
* When the [[Meson spectroscopy|spectroscopic state]] of the meson is known, it is added in parentheses.
* When the spectroscopic state is unknown, mass (in [[Electronvolt#Mass|MeV/''c''<sup>2</sup>]]) is added in parentheses.
* When the meson is in its [[ground state]], nothing is added in parentheses.

==== Flavoured mesons ====
Flavoured mesons are mesons made of pair of quark and antiquarks of different flavours. The rules are simpler in this case: The main symbol depends on the heavier quark, the superscript depends on the charge, and the subscript (if any) depends on the lighter quark. In table form, they are:<ref name=PDGMesonsymbols/>

{|class="wikitable" style="text-align:center;margin:1em auto;"
|+ Nomenclature of flavoured mesons
|-
! rowspan=2 | Quark
! colspan=6 | Antiquark
|-
! up !! down !! charm !! strange !! top !! bottom
|-
| up || {{n/a}} || {{efn|group=lower-roman|name=zero-I3-note|For the purpose of nomenclature, the isospin projection {{mvar|I}}{{sub|3}} is treated as if it were ''not'' a flavour quantum number. This means that the charged pion-like mesons ({{mvar|π}}{{sup|±}}, {{mvar|a}}{{sup|±}}, {{mvar|b}}{{sup|±}}, and {{mvar|ρ}}{{sup|±}} mesons) follow the rules of flavourless mesons, even if they aren't truly "flavourless".}} || {{SubatomicParticle|link=yes|AntiD0}} || {{SubatomicParticle|link=yes|Kaon+}} || {{SubatomicParticle|link=yes|AntiT0}}|| {{SubatomicParticle|link=yes|B+}}
|-
| down || {{efn|group=lower-roman|name=zero-I3-note}} || {{n/a}} || {{SubatomicParticle|link=yes|D-}} || {{SubatomicParticle|link=yes|Kaon0}} || {{SubatomicParticle|link=yes|T-}} || {{SubatomicParticle|link=yes|B0}}
|-
| charm || {{SubatomicParticle|link=yes|D0}} || {{SubatomicParticle|link=yes|D+}} || {{n/a}} || {{SubatomicParticle|link=yes|Strange D+}} || {{SubatomicParticle|link=yes|Charmed AntiT0}}|| {{SubatomicParticle|link=yes|Charmed B+}}
|-
| strange || {{SubatomicParticle|link=yes|Kaon-}} || {{SubatomicParticle|link=yes|AntiKaon0}} || {{SubatomicParticle|link=yes|Strange D-}} || {{n/a}} || {{SubatomicParticle|link=yes|Strange T-}} || {{SubatomicParticle|link=yes|Strange B0}}
|-
| top || {{SubatomicParticle|link=yes|T0}} || {{SubatomicParticle|link=yes|T+}} || {{SubatomicParticle|link=yes|Charmed T0}} || {{SubatomicParticle|link=yes|Strange T+}} || {{n/a}} ||{{SubatomicParticle|link=yes|Bottom T+}}
|-
| bottom || {{SubatomicParticle|link=yes|B-}} || {{SubatomicParticle|link=yes|antiB0}} || {{SubatomicParticle|link=yes|Charmed B-}} || {{SubatomicParticle|link=yes|Strange AntiB0}} || {{SubatomicParticle|link=yes|Bottom T-}} || {{n/a}}
|}

{{reflist|group=lower-roman}}

;In addition:
* If [[Total angular momentum|{{mvar|J}}]]<sup>[[Parity (physics)|P]]</sup> is in the "normal series" (i.e., [[Total angular momentum|{{mvar|J}}]]<sup>[[Parity (physics)|P]]</sup> = 0<sup>+</sup>, 1<sup>−</sup>, 2<sup>+</sup>, 3<sup>−</sup>, ...), a superscript ∗ is added.
* If the meson is not pseudoscalar ([[Total angular momentum|{{mvar|J}}]]<sup>[[Parity (physics)|P]]</sup> = 0<sup>−</sup>) or vector ([[Total angular momentum|{{mvar|J}}]]<sup>[[Parity (physics)|P]]</sup> = 1<sup>−</sup>), {{mvar|J}} is added as a subscript.
* When the [[Meson spectroscopy|spectroscopic state]] of the meson is known, it is added in parentheses.
* When the spectroscopic state is unknown, mass (in [[Electronvolt#Mass|MeV/''c''<sup>2</sup>]]) is added in parentheses.
* When the meson is in its [[ground state]], nothing is added in parentheses.

== Exotic mesons ==
{{main|Exotic meson}}
There is experimental evidence for particles that are [[hadron]]s (i.e., are composed of quarks) and are color-neutral with zero baryon number, and thus by conventional definition are mesons. Yet, these particles do not consist of a single quark/antiquark pair, as all the other conventional mesons discussed above do. A tentative category for these particles is [[exotic meson]]s.

There are at least five exotic meson resonances that have been experimentally confirmed to exist by two or more independent experiments. The most statistically significant of these is the [[Z(4430)]], discovered by the [[Belle experiment]] in 2007 and confirmed by [[LHCb]] in 2014. It is a candidate for being a [[tetraquark]]: a particle composed of two quarks and two antiquarks.<ref name=LHCbZ4430TQuark>LHCb collaborators (2014): [https://arxiv.org/abs/1404.1903 Observation of the resonant character of the Z(4430)− state]</ref> See the main article above for other particle resonances that are candidates for being exotic mesons.

== List ==
{{Main|List of mesons}}

=== Pseudoscalar mesons ===

{| class="wikitable sortable" style="text-align:center;"
|-
! class=unsortable | Particle name
! Particle <br/>symbol
! Antiparticle <br/>symbol
! class=unsortable | Quark <br/>content
! [[Rest mass]] ([[electron volt|MeV]]/[[speed of light|''c'']]<sup>2</sup>)
! width="50" | [[Isospin|I]]<sup>[[G parity|G]]</sup>
! width="50" | [[Total angular momentum|J]]<sup>[[Parity (physics)|P]][[C-parity|C]]</sup>
! width="50" | [[strangeness|S]]
! width="50" | [[charm (quantum number)|C]]
! width="50" | [[bottomness|B']]
! data-sort-type=number | [[Mean lifetime]] ([[second|s]])
! class=unsortable|Commonly decays to <br/>(>5% of decays)
|-
| Pion<ref name=PDGPion+->C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s008.pdf Particle listings – {{Subatomic particle|Pion+-}}]</ref>
| {{Subatomic particle|link=yes|Pion+}}
| {{Subatomic particle|link=yes|Pion-}}
| {{Subatomic particle|link=yes|Up quark}}{{Subatomic particle|link=yes|Down antiquark}}
| {{sort|0139.57018|{{val|139.57018|0.00035}}}}
| 1<sup>&minus;</sup>
| 0<sup>&minus;</sup>
| 0
| 0
| 0
| {{sort|-08.2|{{val|2.6033|0.0005|e=-8}}}}
| {{nowrap|{{Subatomic particle|link=yes|Antimuon}} + {{Subatomic particle|link=yes|Muon neutrino}}}}
|-
| Pion<ref name=PDGPion0>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s009.pdf Particle listings – {{Subatomic particle|Pion0}}]</ref>
| {{Subatomic particle|link=yes|Pion0}}
| {{n/a|Self}}
| <math>\mathrm{\tfrac{u\bar{u} - d\bar{d}}{\sqrt{2}}}\,</math><sup>{{ref|quarkcontent|[a]}}</sup>
| {{sort|0134.9766|{{val|134.9766|0.0006}}}}
| 1<sup>&minus;</sup>
| 0<sup>&minus;+</sup>
| 0
| 0
| 0
| {{sort|-17|{{val|8.4|0.6|e=-17}}}}
| {{nowrap|{{Subatomic particle|link=yes|Photon}} + {{Subatomic particle|link=yes|Photon}}}}
|-
| Eta meson<ref name=PDGEta>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s014.pdf Particle listings – {{Subatomic particle|Eta}}]</ref>
| {{Subatomic particle|link=yes|Eta}}
| {{n/a|Self}}
| {{nowrap|<math>\mathrm{\tfrac{u\bar{u} + d\bar{d} - 2s\bar{s}}{\sqrt{6}}}\,</math><sup>{{ref|quarkcontent|[a]}}</sup>}}
| {{sort|0547.853|{{val|547.853|0.024}}}}
| 0<sup>+</sup>
| 0<sup>&minus;+</sup>
| 0
| 0
| 0
| {{sort|-19|{{val|5.0|0.3|e=-19}}<sup>{{ref|Lifetime|[b]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|Photon}} + {{Subatomic particle|link=yes|Photon}}}} or <br>{{nowrap|{{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Pion0}} or}} <br>{{nowrap|{{Subatomic particle|link=yes|Pion+}} + {{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Pion-}}}}
|-
| Eta prime meson<ref name=PDGEtaPrime>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m002.pdf Particle listings – {{Subatomic particle|Eta prime}}]</ref>
| {{Subatomic particle|link=yes|Eta prime}}(958)
| {{n/a|Self}}
| <math>\mathrm{\tfrac{u\bar{u} + d\bar{d} + s\bar{s}}{\sqrt{3}}}\,</math><sup>{{ref|quarkcontent|[a]}}</sup>
| {{sort|0957.66|{{val|957.66|0.24}}}}
| 0<sup>+</sup>
| 0<sup>&minus;+</sup>
| 0
| 0
| 0
| {{sort|-21|{{val|3.2|0.2|e=-21}}<sup>{{ref|Lifetime|[b]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|Pion+}}  + {{Subatomic particle|link=yes|Pion-}} + {{Subatomic particle|link=yes|Eta}} or}} <br>{{nowrap|({{Subatomic particle|link=yes|rho0}} + {{Subatomic particle|link=yes|Photon}}) / ({{Subatomic particle|link=yes|Pion+}}  + {{Subatomic particle|link=yes|Pion-}} + {{Subatomic particle|link=yes|Photon}}) or}} <br>{{nowrap|{{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Eta}}}}
|-
| Charmed eta meson<ref name=PDGCharmedEta>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m026.pdf Particle listings – {{Subatomic particle|Charmed eta}}]</ref>
| {{Subatomic particle|link=yes|Charmed eta}}(1S)
| {{n/a|Self}}
| {{Subatomic particle|link=yes|charm quark}}{{Subatomic particle|link=yes|charm antiquark}}
| {{val|2980.3|1.2}}
| 0<sup>+</sup>
| 0<sup>&minus;+</sup>
| 0
| 0
| 0
| {{sort|-23|{{val|2.5|0.3|e=-23}}<sup>{{ref|Lifetime|[b]}}</sup>}}
| [http://pdg.lbl.gov/2008/listings/m026.pdf See {{Subatomic particle|Charmed eta}} decay modes]
|-
| Bottom eta meson<ref name=PDGBottomEta>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m171.pdf Particle listings – {{Subatomic particle|Bottom eta}}]</ref>
| {{Subatomic particle|link=yes|Bottom eta}}(1S)
| {{n/a|Self}}
| {{Subatomic particle|link=yes|Bottom quark}}{{Subatomic particle|link=yes|Bottom antiquark}}
| {{val|9300|40}}
| <span style="color:red">0</span><sup><span style="color:red">+</span></sup>
| <span style="color:red">0</span><sup><span style="color:red">&minus;+</span></sup>
| 0
| 0
| 0
| Unknown
| [http://pdg.lbl.gov/2008/listings/m171.pdf See {{Subatomic particle|Bottom eta}} decay modes]
|-
| Kaon<ref name=PDGKaon+>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s010.pdf Particle listings – {{Subatomic particle|Kaon+-}}]</ref>
| {{Subatomic particle|link=yes|Kaon+}}
| {{Subatomic particle|link=yes|Kaon-}}
| {{Subatomic particle|link=yes|Up quark}}{{Subatomic particle|link=yes|Strange antiquark}}
| {{sort|0493.677|{{val|493.677|0.016}}}}
| {{frac|1|2}}
| 0<sup>&minus;</sup>
| 1
| 0
| 0
| {{sort|-08.3|{{val|1.2380|0.0021|e=-8}}}}
| {{nowrap|{{Subatomic particle|link=yes|Antimuon}} + {{Subatomic particle|link=yes|Muon neutrino}} or}}<br>
{{nowrap|{{Subatomic particle|link=yes|pion+}} + {{Subatomic particle|link=yes|pion0}} or}} <br> {{nowrap|{{Subatomic particle|link=yes|Pion+}} + {{Subatomic particle|link=yes|Pion+}} + {{Subatomic particle|link=yes|Pion-}} or}} <br> {{nowrap|{{Subatomic particle|link=yes|pion0}} + {{Subatomic particle|link=yes|positron}} + {{Subatomic particle|link=yes|Electron neutrino}}}}
|-
| Kaon<ref name=PDGKaon0>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s011.pdf Particle listings – {{Subatomic particle|Kaon0}}]</ref>
| {{Subatomic particle|link=yes|Kaon0}}
| {{Subatomic particle|link=yes|Antikaon0}}
| {{Subatomic particle|link=yes|Down quark}}{{Subatomic particle|link=yes|Strange antiquark}}
| {{sort|0497.614|{{val|497.614|0.024}}}}
| {{frac|1|2}}
| 0<sup>&minus;</sup>
| 1
| 0
| 0
| <sup>{{ref|strongforce|[c]}}</sup>
| <sup>{{ref|strongforce|[c]}}</sup>
|-
| K-Short<ref name=PDGK-short>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s012.pdf Particle listings – {{Subatomic particle|K-short0}}]</ref>
| {{Subatomic particle|link=yes|K-short0}}
| {{n/a|Self}}
| <math>\mathrm{\tfrac{d\bar{s} + s\bar{d}}{\sqrt{2}}}\,</math><sup>{{ref|Kaon|[e]}}</sup>
| {{sort|0497.614|{{val|497.614|0.024}}}}<sup>{{ref|Kaonmass|[d]}}</sup>
| {{frac|1|2}}
| 0<sup>&minus;</sup>
| [[List of mesons#Notes on neutral kaons|(*)]]
| 0
| 0
| {{sort|-11|{{val|8.953|0.005|e=-11}}}}
| {{nowrap|{{Subatomic particle|link=yes|pion+}} + {{Subatomic particle|link=yes|pion-}} or}} <br>{{nowrap|{{Subatomic particle|link=yes|pion0}} + {{Subatomic particle|link=yes|pion0}}}}
|-
| K-Long<ref name=PDGK-long>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s013.pdf Particle listings – {{Subatomic particle|k-long0}}]</ref>
| {{Subatomic particle|link=yes|K-long0}}
| {{n/a|Self}}
| <math>\mathrm{\tfrac{d\bar{s} - s\bar{d}}{\sqrt{2}}}\,</math><sup>{{ref|Kaon|[e]}}</sup>
| {{sort|0497.614|{{val|497.614|0.024}}}}<sup>{{ref|Kaonmass|[d]}}</sup>
| {{frac|1|2}}
| 0<sup>&minus;</sup>
| [[List of mesons#Notes on neutral kaons|(*)]]
| 0
| 0
| {{sort|-08.1|{{val|5.116|0.020|e=-8}}}}
| {{nowrap|{{Subatomic particle|link=yes|Pion+-}} + {{Subatomic particle|link=yes|electron-+}} + {{Subatomic particle|link=yes|Electron neutrino}} or}}<br> {{nowrap|{{Subatomic particle|link=yes|Pion+-}} + {{Subatomic particle|link=yes|muon-+}} + {{Subatomic particle|link=yes|Muon neutrino}} or}} <br>{{nowrap|{{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Pion0}} or}} <br>{{nowrap|{{Subatomic particle|link=yes|Pion+}} + {{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Pion-}}}}
|-
| D meson<ref name=PDGD+>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s031.pdf Particle listings – {{Subatomic particle|D+-}}]</ref>
| {{Subatomic particle|link=yes|D+}}
| {{Subatomic particle|link=yes|D-}}
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|Down antiquark}}
| {{val|1869.62|0.20}}
| {{frac|1|2}}
| 0<sup>&minus;</sup>
| 0
| +1
| 0
| {{sort|-12.4|{{val|1.040|0.007|e=-12}}}}
| [http://pdg.lbl.gov/2008/listings/s031.pdf See {{Subatomic particle|D+}} decay modes]
|-
| D meson<ref name=PDGD0>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s032.pdf Particle listings – {{Subatomic particle|D0}}]</ref>
| {{Subatomic particle|link=yes|D0}}
| {{Subatomic particle|link=yes|AntiD0}}
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|up antiquark}}
| {{val|1864.84|0.17}}
| {{frac|1|2}}
| 0<sup>&minus;</sup>
| 0
| +1
| 0
| {{sort|-13.3|{{val|4.101|0.015|e=-13}}}}
| [http://pdg.lbl.gov/2008/listings/s032.pdf See {{Subatomic particle|D0}} decay modes]
|-
| strange D meson<ref name=PDGDs>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s034.pdf Particle listings – {{Subatomic particle|Strange D+-}}]</ref>
| {{Subatomic particle|link=yes|Strange D+}}
| {{Subatomic particle|link=yes|Strange D-}}
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|strange antiquark}}
| {{val|1968.49|0.34}}
| 0
| 0<sup>&minus;</sup>
| +1
| +1
| 0
| {{sort|-13.1|{{val|5.00|0.07|e=-13}}}}
| [http://pdg.lbl.gov/2008/listings/s034.pdf See {{Subatomic particle|Strange D+}} decay modes]
|-
| B meson<ref name=PDGB+>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s041.pdf Particle listings – {{Subatomic particle|B+-}}]</ref>
| {{Subatomic particle|link=yes|B+}}
| {{Subatomic particle|link=yes|B-}}
| {{Subatomic particle|link=yes|up quark}}{{Subatomic particle|link=yes|bottom antiquark}}
| {{val|5279.15|0.31}}
| <span style="color:red">{{frac|1|2}}</span>
| <span style="color:red">0</span><sup><span style="color:red">&minus;</span></sup>
| 0
| 0
| +1
| {{sort|-12.1|{{val|1.638|0.011|e=-12}}}}
| [http://pdg.lbl.gov/2008/listings/s041.pdf See {{Subatomic particle|B+}} decay modes]
|-
| B meson<ref name=PDGB0>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s042.pdf Particle listings – {{Subatomic particle|B0}}]</ref>
| {{Subatomic particle|link=yes|B0}}
| {{Subatomic particle|link=yes|AntiB0}}
| {{Subatomic particle|link=yes|Down quark}}{{Subatomic particle|link=yes|Bottom antiquark}}
| {{val|5279.53|33}}
| <span style="color:red">{{frac|1|2}}</span>
| <span style="color:red">0</span><sup><span style="color:red">&minus;</span></sup>
| 0
| 0
| +1
| {{sort|-12.2|{{val|1.530|0.009|e=-12}}}}
| [http://pdg.lbl.gov/2008/listings/s042.pdf See {{Subatomic particle|B0}} decay modes]
|-
| Strange B meson<ref name=PDGBs>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s086.pdf Particle listings – {{Subatomic particle|Strange B0}}]</ref>
| {{Subatomic particle|link=yes|Strange B0}}
| {{Subatomic particle|link=yes|Strange AntiB0}}
| {{Subatomic particle|link=yes|strange quark}}{{Subatomic particle|link=yes|Bottom antiquark}}
| {{val|5366.3|0.6}}
| <span style="color:red">0</span>
| <span style="color:red">0</span><sup><span style="color:red">&minus;</span></sup>
| &minus;1
| 0
| +1
| {{sort|-12.3|{{val|1.470|+0.026|-0.027|e=-12}}}}
| [http://pdg.lbl.gov/2008/listings/s086.pdf See {{Subatomic particle|Strange B0}} decay modes]
|-
| Charmed B meson<ref name=PDGBc>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s091.pdf Particle listings – {{Subatomic particle|Charmed B+-}}]</ref>
| {{Subatomic particle|link=yes|Charmed B+}}
| {{Subatomic particle|link=yes|Charmed B-}}
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|bottom antiquark}}
| {{val|6276|4}}
| <span style="color:red">0</span>
| <span style="color:red">0</span><sup><span style="color:red">&minus;</span></sup>
| 0
| +1
| +1
| {{sort|-13.2|{{val|4.6|0.7|e=-13}}}}
| style="text-align:center;" | [http://pdg.lbl.gov/2008/listings/s091.pdf See {{Subatomic particle|Charmed B+}} decay modes]
|}
<sup>[a]</sup> {{note|quarkcontent}} Makeup inexact due to non-zero quark masses.<br>
<sup>[b]</sup> {{note|Lifetime}} PDG reports the [[resonance width]] (Γ). Here the conversion τ&nbsp;=&nbsp;{{frac|ħ|&Gamma;}} is given instead.<br>
<sup>[c]</sup> {{note|strongforce}}[[Strong force|Strong]] [[eigenstate]]. No definite lifetime (see [[List of mesons#Notes on neutral kaons|kaon notes]] below)<br>
<sup>[d]</sup> {{note|Kaonmass}} The mass of the {{Subatomic particle|K-long0}} and {{Subatomic particle|K-short0}} are given as that of the {{Subatomic particle|Kaon0}}. However, it is known that a difference between the masses of the {{Subatomic particle|K-long0}} and {{Subatomic particle|K-short0}} on the order of {{val|2.2|e=-11|u=MeV/c2}} exists.<ref name=PDGK-long/><br>
<sup>[e]</sup> {{note|Kaon}}[[Weak force|Weak]] [[eigenstate]]. Makeup is missing small [[CP violation|CP–violating]] term (see [[List of mesons#Notes on neutral kaons|notes on neutral kaons]] below).

=== Vector mesons ===

{| class="wikitable sortable" style="text-align:center;"
|-
! class=unsortable | Particle <br/>name
! Particle <br/>symbol
! Antiparticle <br/>symbol
! class=unsortable | Quark<br/>content
! [[Rest mass]] ([[electron volt|MeV]]/[[speed of light|''c'']]<sup>2</sup>)
! width="50" | [[Isospin|I]]<sup>[[G parity|G]]</sup>
! width="50" | [[Total angular momentum|J]]<sup>[[Parity (physics)|P]][[C-parity|C]]</sup>
! width="50" | [[strangeness|S]]
! width="50" | [[charm (quantum number)|C]]
! width="50" | [[bottomness|B']]
! [[Mean lifetime]] ([[second|s]])
! class=unsortable | Commonly decays to <br/>(>5% of decays)
|-
| Charged rho meson<ref name=PDGRho>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m009.pdf Particle listings – {{Subatomic particle|rho}}]</ref>
| {{Subatomic particle|link=yes|Rho+}}(770)
| {{Subatomic particle|link=yes|Rho-}}(770)
| {{Subatomic particle|link=yes|Up quark}}{{Subatomic particle|link=yes|Down antiquark}}
| {{sort|0775.4|{{val|775.4|0.4}}}}
| 1<sup>+</sup>
| 1<sup>&minus;</sup>
| 0
| 0
| 0
| {{sort|-24|~{{val|4.5|e=-24}}<sup>{{ref|Lifetime2|[f]}}{{ref|Lifetime3|[g]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|Pion+-}} + {{Subatomic particle|link=yes|Pion0}}}}
|-
| Neutral rho meson<ref name=PDGRho/>
| {{Subatomic particle|link=yes|Rho0}}(770)
| {{n/a|Self}}
| {{nowrap|<math>\mathrm{\tfrac{u\bar{u}-d\bar{d}}{\sqrt 2}}</math>}}
| {{sort|0775.49|{{val|775.49|0.34}}}}
| 1<sup>+</sup>
| 1<sup>&minus;&minus;</sup>
| 0
| 0
| 0
| {{sort|-24|~{{val|4.5|e=-24}}<sup>{{ref|Lifetime2|[f]}}{{ref|Lifetime3|[g]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|Pion+}} + {{Subatomic particle|link=yes|Pion-}}}}
|-
| Omega meson<ref name=PDGOmegaMeson>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m001.pdf Particle listings – {{Subatomic particle|Omega meson}}(782)]</ref>
| {{Subatomic particle|link=yes|omega meson}}(782)
| {{n/a|Self}}
| {{nowrap|<math>\mathrm{\tfrac{u\bar{u} + d\bar{d}}{\sqrt{2}}}</math>}}
| {{val|782.65|0.12}}
| 0<sup>&minus;</sup>
| 1<sup>&minus;&minus;</sup>
| 0
| 0
| 0
| {{sort|-23|{{val|7.75|0.07|e=-23}}<sup>{{ref|Lifetime2|[f]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|Pion+}} + {{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Pion-}} or}} <br>{{nowrap|{{Subatomic particle|link=yes|Pion0}} + {{Subatomic particle|link=yes|Photon}}}}
|-
| Phi meson<ref name=PDGPhi>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m004.pdf  Particle listings – {{Subatomic particle|Phi meson}}]</ref>
| {{Subatomic particle|link=yes|Phi meson}}(1020)
| {{n/a|Self}}
| {{Subatomic particle|link=yes|Strange quark}}{{Subatomic particle|link=yes|Strange antiquark}}
| {{val|1019.445|0.020}}
| 0<sup>&minus;</sup>
| 1<sup>&minus;&minus;</sup>
| 0
| 0
| 0
| {{sort|-22.3|{{val|1.55|0.01|e=-22}}<sup>{{ref|Lifetime2|[f]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|Kaon+}} + {{Subatomic particle|link=yes|Kaon-}} or}} <br>{{nowrap|{{Subatomic particle|link=yes|K-short0}} + {{Subatomic particle|link=yes|K-long0}} or}} <br>{{nowrap|({{Subatomic particle|link=yes|rho}} + {{Subatomic particle|link=yes|pion}}) / ({{Subatomic particle|link=yes|pion+}} + {{Subatomic particle|link=yes|pion0}} + {{Subatomic particle|link=yes|pion-}})}}
|-
| J/Psi<ref name="PDGJ/Psi">C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m070.pdf Particle listings – J/&Psi;]</ref>
| {{Subatomic particle|link=yes|J/Psi}}
| {{n/a|Self}}
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|Charm antiquark}}
| {{val|3096.916|0.011}}
| 0<sup>&minus;</sup>
| 1<sup>&minus;&minus;</sup>
| 0
| 0
| 0
| {{sort|-21.1|{{val|7.1|0.2|e=-21}}<sup>{{ref|Lifetime2|[f]}}</sup>}}
| [http://pdg.lbl.gov/2008/listings/m070.pdf See {{Subatomic particle|J/psi}}(1S) decay modes]
|-
| Upsilon meson<ref name=PDGUpsilon>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m049.pdf Particle listings – {{Subatomic particle|Upsilon}}(1S)]</ref>
| {{Subatomic particle|link=yes|Upsilon}}(1S)
| {{n/a|Self}}
| {{Subatomic particle|link=yes|bottom quark}}{{Subatomic particle|link=yes|bottom antiquark}}
| {{val|9460.30|0.26}}
| 0<sup>&minus;</sup>
| 1<sup>&minus;&minus;</sup>
| 0
| 0
| 0
| {{sort|-20.3|{{val|1.22|0.03|e=-20}}<sup>{{ref|Lifetime2|[f]}}</sup>}}
| [http://pdg.lbl.gov/2008/listings/m049.pdf See {{Subatomic particle|Upsilon}}(1S) decay modes]
|-
| Kaon<ref name=PDGKaon*>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m018.pdf Particle listings – {{Subatomic particle|Kaon*}}(892)]</ref>
| {{Subatomic particle|link=yes|Kaon*+}}
| {{Subatomic particle|link=yes|Kaon*-}}
| {{Subatomic particle|link=yes|Up quark}}{{Subatomic particle|link=yes|Strange antiquark}}
| {{val|891.66|0.026}}
| {{frac|1|2}}
| 1<sup>&minus;</sup>
| 1
| 0
| 0
| {{sort|-20.1|~{{val|1.3|e=-23}}<sup>{{ref|Lifetime2|[f]}}{{ref|Lifetime3|[g]}}</sup>}}
| [http://pdg.lbl.gov/2008/listings/m018.pdf See {{Subatomic particle|Kaon*}}(892) decay modes]
|-
| Kaon<ref name=PDGKaon*/>
| {{Subatomic particle|link=yes|Kaon*0}}
| {{Subatomic particle|link=yes|Antikaon*0}}
| {{Subatomic particle|link=yes|Down quark}}{{Subatomic particle|link=yes|Strange antiquark}}
| {{val|896.00|0.025}}
| {{frac|1|2}}
| 1<sup>&minus;</sup>
| 1
| 0
| 0
| {{sort|-20.2|~{{val|1.3|e=-23}}<sup>{{ref|Lifetime2|[f]}}</sup>}}
| [http://pdg.lbl.gov/2008/listings/m018.pdf See {{Subatomic particle|Kaon*}}(892) decay modes]
|-
| D meson<ref name=PDGD*+>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m062.pdf Particle listings – {{Subatomic particle|D*+-}}(2010)]</ref>
| {{Subatomic particle|link=yes|D*+}}(2010)
| {{Subatomic particle|link=yes|D*-}}(2010)
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|Down antiquark}}
| {{val|2010.27|0.17}}
| <span style="color:red">{{frac|1|2}}</span>
| <span style="color:red">1</span><sup><span style="color:red">&minus;</span></sup>
| 0
| +1
| 0
| {{sort|-21.2|{{val|6.9|1.9|e=-21}}<sup>{{ref|Lifetime2|[f]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|D0}} + {{Subatomic particle|link=yes|Pion+}} or}} <br/>{{nowrap|{{Subatomic particle|link=yes|D+}} + {{Subatomic particle|link=yes|Pion0}}}}
|-
| D meson<ref name=PDGD*0>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/m061.pdf Particle listings – {{Subatomic particle|D*0}}(2007)]</ref>
| {{Subatomic particle|link=yes|D*0}}(2007)
| {{Subatomic particle|link=yes|AntiD*0}}(2007)
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|up antiquark}}
| {{val|2006.97|0.19}}
| <span style="color:red">{{frac|1|2}}</span>
| <span style="color:red">1</span><sup><span style="color:red">&minus;</span></sup>
| 0
| +1
| 0
| {{sort|-22.2|>{{val|3.1|e=-22}}<sup>{{ref|Lifetime2|[f]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|D0}} + {{Subatomic particle|link=yes|Pion0}} or}} <br/>{{nowrap|{{Subatomic particle|link=yes|D0}} + {{Subatomic particle|link=yes|Photon}}}}
|-
| strange D meson<ref name=PDGD*s>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s074.pdf Particle listings – {{Subatomic particle|Strange D*+-}}]</ref>
| {{Subatomic particle|link=yes|Strange D*+}}
| {{Subatomic particle|link=yes|Strange D*-}}
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|strange antiquark}}
| {{val|2112.3|0.5}}
| <span style="color:red">0</span>
| <span style="color:red">1</span><sup><span style="color:red">&minus;</span></sup>
| +1
| +1
| 0
| {{sort|-22.1|>{{val|3.4|e=-22}}<sup>{{ref|Lifetime2|[f]}}</sup>}}
| {{nowrap|{{Subatomic particle|link=yes|D*+}} + {{Subatomic particle|link=yes|Photon}} or}} <br>{{nowrap|{{Subatomic particle|link=yes|D*+}} + {{Subatomic particle|link=yes|Pion0}}}}
|-
| B meson<ref name=PDGB*>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s085.pdf Particle listings – {{Subatomic particle|B*}}]</ref>
| {{Subatomic particle|link=yes|B*+}}
| {{Subatomic particle|link=yes|B*-}}
| {{Subatomic particle|link=yes|up quark}}{{Subatomic particle|link=yes|bottom antiquark}}
| {{val|5325.1|0.5}}
| <span style="color:red">{{frac|1|2}}</span>
| <span style="color:red">1</span><sup><span style="color:red">&minus;</span></sup>
| 0
| 0
| +1
| Unknown
| {{nowrap|{{Subatomic particle|link=yes|B+}} + {{Subatomic particle|link=yes|Photon}}}}
|-
| B meson<ref name=PDGB*/>
| {{Subatomic particle|link=yes|B*0}}
| {{Subatomic particle|link=yes|AntiB*0}}
| {{Subatomic particle|link=yes|Down quark}}{{Subatomic particle|link=yes|Bottom antiquark}}
| {{val|5325.1|0.5}}
| <span style="color:red">{{frac|1|2}}</span>
| <span style="color:red">1</span><sup><span style="color:red">&minus;</span></sup>
| 0
| 0
| +1
| Unknown
| {{nowrap|{{Subatomic particle|link=yes|B0}} + {{Subatomic particle|link=yes|Photon}}}}
|-
| Strange B meson<ref name=PDGBs*>C. Amsler ''et al''. (2008): [http://pdg.lbl.gov/2008/listings/s087.pdf Particle listings – {{Subatomic particle|Strange B*}}]</ref>
| {{Subatomic particle|link=yes|Strange B*0}}
| {{Subatomic particle|link=yes|Strange AntiB*0}}
| {{Subatomic particle|link=yes|strange quark}}{{Subatomic particle|link=yes|Bottom antiquark}}
| {{val|5412.8|1.3}}
| <span style="color:red">0</span>
| <span style="color:red">1</span><sup><span style="color:red">&minus;</span></sup>
| &minus;1
| 0
| +1
| Unknown
| {{nowrap|{{Subatomic particle|link=yes|Strange B0}}+{{Subatomic particle|link=yes|Photon}}}}
|-
| Charmed B meson<sup>†</sup>
| {{Subatomic particle|link=yes|Charmed B*+}}
| {{Subatomic particle|link=yes|Charmed B*-}}
| {{Subatomic particle|link=yes|Charm quark}}{{Subatomic particle|link=yes|bottom antiquark}}
| Unknown
| <span style="color:red">0</span>
| <span style="color:red">1</span><sup><span style="color:red">&minus;</span></sup>
| 0
| +1
| +1
| Unknown
| Unknown
|}
<sup>[f]</sup> {{note|Lifetime2}} PDG reports the [[resonance width]] (Γ). Here the conversion τ&nbsp;=&nbsp;{{frac|ħ|&Gamma;}} is given instead.<br>
<sup>[g]</sup> {{note|Lifetime3}} The exact value depends on the method used. See the given reference for detail.

=== Notes on neutral kaons ===
There are two complications with [[Electric charge|neutral]] [[kaon]]s:<ref name="Cronin"/>
* Due to [[Kaon#Neutral kaon mixing|neutral kaon mixing]], the {{Subatomic particle|link=yes|K-short0}} and {{Subatomic particle|link=yes|K-long0}} are not [[eigenstate]]s of [[strangeness]].  However, they ''are'' eigenstates of the [[weak force]], which determines how they [[Radioactive decay|decay]], so these are the particles with definite [[Mean lifetime|lifetime]].
* The [[linear combination]]s given in the table for the {{Subatomic particle|link=yes|K-short0}} and {{Subatomic particle|link=yes|K-long0}} are not exactly correct, since there is a small correction due to [[CP violation]].  See [[Kaon#CP violation|CP violation in kaons]].

Note that these issues also exist in principle for other neutral, [[flavour (particle physics)|flavored]] mesons; however, the weak eigenstates are considered separate particles only for kaons because of their dramatically different lifetimes.<ref name="Cronin">J.W. Cronin (1980)</ref>

== See also ==
* [[Mesonic molecule]]
* [[Standard Model]]

== Footnotes ==
{{notelist|group=upper-alpha}}

== References ==
{{reflist|22em|refs=

<ref name=Amsler-etal-PDG-2008>
{{cite journal
 |last1=Amsler |first1=C.
 |collaboration=[[Particle Data Group]]
 |display-authors=etal
 |year=2008
 |title=Review of Particle Physics
 |journal=[[Physics Letters B]]
 |volume=667 |issue=1 |pages=1–1340
 |bibcode = 2008PhLB..667....1A
 |doi=10.1016/j.physletb.2008.07.018
 |pmid=10020536 |hdl=1854/LU-685594
 |s2cid=227119789
 |url=http://scipp.ucsc.edu/%7Ehaber/pubs/Review_of_Particle_Physics_2014.pdf
}}
</ref>

<ref name="J.J. Aubert ''et al.'' (1974)">
{{cite journal
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 |first3=P.   |last3=Biggs        |first4=J.  |last4=Burger
 |first5=M.   |last5=Chen         |first6=G.  |last6=Everhart
 |first7=P.   |last7=Goldhagen    |first8=J.  |last8=Leong
 |first9=T.   |last9=McCorriston  |first10=T. |last10=Rhoades
 |first11=M.  |last11=Rohde       |first12=Samuel |last12=Ting
 |first13=Sau |last13=Wu          |first14=Y. |last14=Lee 
 |display-authors=6
 |year=1974
 |title=Experimental observation of a Heavy Particle ''J''
 |journal=[[Physical Review Letters]]
 |volume=33 |issue=23 |pages=1404–1406
 |bibcode = 1974PhRvL..33.1404A
 |doi=10.1103/PhysRevLett.33.1404 |doi-access=free
}}
</ref>

<ref name="J.E. Augustin ''et al.'' (1974)">
{{cite journal
 |last1=Augustin |first1=J.E. |last2=Boyarski |first2=A.
 |last3=Breidenbach |first3=M. |last4=Bulos |first4=F.
 |last5=Dakin |first5=J. |last6=Feldman |first6=G.
 |last7=Fischer |first7=G. |last8=Fryberger |first8=D.
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 |last19=Rapidis |first19=P. |last20=Schwitters |first20=R.
 |last21=Tanenbaum |first21=W. |last22=Vannucci |first22=F.
 |last23=Abrams |first23=G. |last24=Briggs |first24=D.
 |last25=Chinowsky |first25=W. |last26=Friedberg |first26=C.
 |last27=Goldhaber |first27=G. |last28=Hollebeek |first28=R.
 |last29=Kadyk |first29=J. |last30=Lulu |first30=B.
 |display-authors=6
 |year=1974
 |title=Discovery of a narrow resonance in e{{sup|+}}e{{sup|−}} annihilation
 |journal=[[Physical Review Letters]]
 |volume=33 |issue=23 |pages=1406–1408
 |bibcode = 1974PhRvL..33.1406A
 |doi=10.1103/PhysRevLett.33.1406 |doi-access=free
}}
</ref>

<ref name="S.W. Herb ''et al.'' (1977)">
{{cite journal
 |last1=Herb |first1=S. W. |last2=Hom |first2=D.
 |last3=Lederman |first3=L. |last4=Sens |first4=J.
 |last5=Snyder |first5=H. |last6=Yoh |first6=J.
 |last7=Appel |first7=J. |last8=Brown |first8=B.
 |last9=Brown |first9=C. |last10=Innes |first10=W.
 |last11=Ueno |first11=K. |last12=Yamanouchi |first12=T.
 |last13=Ito |first13=A. |last14=Jöstlein |first14=H.
 |last15=Kaplan |first15=D. |last16=Kephart |first16=R.
 |display-authors=6
 |year=1977
 |title=Observation of a di-muon resonance at 9.5&nbsp;GeV in 400&nbsp;GeV proton-nucleus collisions
 |journal=[[Physical Review Letters]]
 |volume=39 |issue=5 |pages=252–255
 |bibcode = 1977PhRvL..39..252H|osti=1155396
 |doi=10.1103/PhysRevLett.39.252 
}}
</ref>

}} <!-- end "refs=" -->

<!-- unused 
== General Sources ==
{{refbegin}}
* {{cite journal |last1=Heisenberg |first1=W. |title=Über den Bau der Atomkerne I |year=1932 |journal=[[Zeitschrift für Physik]] |language=de |volume=77 |issue=1–2 |pages=1–11 |bibcode = 1932ZPhy...77....1H |doi=10.1007/BF01342433 |s2cid=186218053 }}
* {{cite journal |last1=Heisenberg |first1=W. |title=Über den Bau der Atomkerne II |year=1932 |journal=[[Zeitschrift für Physik]] |language=de |volume=78 |issue=3–4 |pages=156–164 |bibcode = 1932ZPhy...78..156H |doi=10.1007/BF01337585 |s2cid=186221789 }}
* {{cite journal |last1=Heisenberg |first1=W. |title=Über den Bau der Atomkerne III |year=1932 |journal=[[Zeitschrift für Physik]] |language=de |volume=80 |issue=9–10 |pages=587–596 |bibcode = 1933ZPhy...80..587H |doi=10.1007/BF01335696 |s2cid=126422047 }}
* {{cite journal |last1=Ahmad |first1=Ishfaq |author-link=Ishfaq Ahmad |year=1965 |title=The Interactions of 200&nbsp;MeV π± -Mesons with Complex Nuclei Proposal to Study the Interactions of 200&nbsp;MeV π± -Mesons with Complex Nuclei | url = http://cdsweb.cern.ch/record/1117270/files/CM-P00073662.pdf |journal=CERN Documents |volume=3 |issue=5 }}
* {{cite book |last1=Shankar |first1=R. |year=1994 |title=Principles of Quantum Mechanics |edition=2nd |location=New York |publisher=Plenum Press |isbn=0-306-44790-8 }}
* {{cite book |last1=Sozzi |first1=M. S. |year=2008a |title=Discrete Symmetries and CP Violation: From Experiment to Theory |url=https://archive.org/details/discretesymmetri00msoz |url-access=limited |publisher=Oxford University Press |isbn=978-0-19-929666-8 |pages=[https://archive.org/details/discretesymmetri00msoz/page/n31 15]–87 |chapter=Parity }}

{{refend}}
-->

== External links ==
* {{cite web
 |title=A table of some mesons and their properties
 |editor=Nave, C.R.
 |year=2005
 |website=Hyperphysics
 |department=Department of Physics and Astronomy
 |publisher=[[Georgia State University]]
 |place=Atlanta, GA
 |url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/meson.html#c1
}}
* {{cite web
 |title=Particle Data Group
 |type=main page
 |website=[[Lawrence Berkeley Laboratory]]
 |place=Lawrence, CA
 |url=http://pdg.lbl.gov
}} — Compiles authoritative information on particle properties
* {{cite book
 |last1=van Beveren |first1=E.
 |last2=Rupp |first2=G.
 |last3=Petropoulos |first3=N.
 |last4=Kleefeld |first4=F.
 |date=2003
 |chapter=The light scalar mesons within quark models
 |title=Hadron Physics: Effective Theories of Low Energy QCD
 |series=AIP Conference Proceedings
 |volume=660 |pages=353–366
 |doi=10.1063/1.1570585
 |arxiv=hep-ph/0211411
 |bibcode=2003AIPC..660..353V 
 |s2cid=6295609 
 }}
* {{cite web
 |title=Naming scheme for hadrons
 |year=2004
 |website=[[Particle Data Group]]
 |place=Lawrence, CA
 |publisher=[[Lawrence Berkeley Laboratory]]
 |url=http://pdg.lbl.gov/2004/reviews/namingrpp.pdf
}}
* {{cite web
 |title=Mesons made thinkable
 |website=thingsmadethinkable.com
 |url=http://www.thingsmadethinkable.com/item/mesons.php
}} — An interactive visualisation allowing physical properties to be compared
* {{cite press release
 |author=Perricone, Mike 
 |date=22 March 2006
 |title=What happened to the antimatter? Fermilab's DZero experiment finds clues in quick-change meson
 |publisher=[[Fermi National Accelerator Laboratory]] (Fermilab)
 |place=Batavia, IL
 |url=https://news.fnal.gov/2006/03/happened-antimatter-fermilabs-dzero-experiment-finds-clues-quick-change-meson/ <!-- http://www.fnal.gov/pub/presspass/press_releases/DZeroB_s.html -->
}}
* {{cite press release
 |author=Perricone, Mike 
 |date=25 September 2006
 |title=Fermilab's CDF scientists make it official: They have discovered the quick-change behavior of the B-sub-s meson, which switches between matter and antimatter 3&nbsp;trillion times a second
 |publisher=[[Fermi National Accelerator Laboratory]] (Fermilab)
 |place=Batavia, IL
 |url=http://www.fnal.gov/pub/presspass/press_releases/CDF_meson.html
}}

== Further reading ==

* Pauli, Wolfgang  (1948) ''Meson Theory of Nuclear Forces,'' Interscience Publishers, Inc. New York 
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[[Category:Mesons| ]]
[[Category:Bosons]]
[[Category:Hadrons]]
[[Category:Force carriers]]