Meson

This article is about the subatomic particle. For the software, seeMeson (software).

Mesons

Mesons of spin 0 form anonet
Composition	composite:quarksandantiquarks
Statistics	bosonic
Family	hadron
Interactions	strong,weak,electromagneticandgravity
Theorized	Hideki Yukawa(1935)
Discovered	1947
Types	~140 (List)
Mass	from 134.9 MeV/c2( π0 ) to 9.460 GeV/c2( ϒ )
Electric charge	−1e,0e,+1e
Spin	0ħ,1ħ

Inparticle physics,ameson(/ˈmiːzɒn,ˈmɛzɒn/) is a type ofhadronicsubatomic particlecomposed of an equal number ofquarksandantiquarks,usually one of each, bound together by thestrong interaction.Because mesons are composed of quark subparticles, they have a meaningful physical size, a diameter of roughly onefemtometre(10⁻¹⁵m),which is about 0.6 times the size of aprotonorneutron.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 stableelectrons,neutrinosandphotons.

Outside the nucleus, mesons appear in nature only as short-lived products of very high-energy collisions between particles made of quarks, such ascosmic rays(high-energy protons and neutrons) andbaryonic matter.Mesons are routinely produced artificially incyclotronsor otherparticle acceleratorsin the collisions of protons,antiprotons,or other particles.

Higher-energy (more massive) mesons were created momentarily in theBig 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 thehadronparticle family, which are defined simply as particles composed of two or more quarks. The other members of the hadron family are thebaryons:subatomic particles composed of odd numbers of valence quarks (at least three), and some experiments show evidence ofexotic mesons,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 spin⁠1/2⁠,the difference in quark number between mesons and baryons results in conventional two-quark mesons beingbosons,whereas baryons arefermions.

Each type of meson has a correspondingantiparticle(antimeson) in which quarks are replaced by their corresponding antiquarks and vice versa. For example, a positivepion(
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.

Because mesons are composed of quarks, they participate in both theweak interactionandstrong interaction.Mesons with netelectric chargealso participate in theelectromagnetic interaction.Mesons are classified according to their quark content,total angular momentum,parityand various other properties, such asC-parityandG-parity.Although no meson is stable, those of lowermassare nonetheless more stable than the more massive, and hence are easier to observe and study inparticle acceleratorsor incosmic rayexperiments. 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, theJ/Psi meson(
J/ψ
) containing thecharm quark,first seen 1974,is about three times as massive as a proton, and theupsilon meson(
ϒ
) containing thebottom quark,first seen in 1977,is about ten times as massive as a proton.

History

From theoretical considerations, in 1934Hideki Yukawapredicted the existence and the approximate mass of the "meson" as the carrier of thenuclear forcethat holdsatomic nucleitogether.If there were no nuclear force, all nuclei with two or moreprotonswould fly apart due toelectromagneticrepulsion.Yukawacalled his carrier particle the meson, from μέσοςmesos,theGreekword for "intermediate", because its predicted mass was between that of the electron and that of the proton, which has about 1,836 times the mass of the electron.YukawaorCarl David Anderson,who discovered themuon,had originally named the particle the "mesotron", but he was corrected by the physicistWerner Heisenberg(whose father was a professor of Greek at theUniversity of Munich). Heisenberg pointed out that there is no "tr" in the Greek word "mesos".

The first candidate for Yukawa's meson, in modern terminology known as themuon,was discovered in 1936 byCarl David Andersonand others in thedecay productsof cosmic ray interactions. The"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"mu meson"did not participate in the strong nuclear interaction at all, but rather behaved like a heavy version of theelectron,and was eventually classed as aleptonlike 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 duringWorld War II(1939–1945), with most physicists working in applied projects for wartime necessities. When the war ended in August 1945, many physicists gradually returned to peacetime research. The first true meson to be discovered was what would later be called the"pi meson"(or pion). During 1939–1942,Debendra Mohan BoseandBibha ChowdhuriexposedIlfordhalf-tonephotographic plates in the high altitude mountainous regions ofDarjeeling,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 inNature,they identified a cosmic particle having an average mass close to 200 times the mass of electron.This discovery was made in 1947 with improved full-tone photographic emulsion plates, byCecil Powell,Hugh Muirhead,César Lattes,andGiuseppe Occhialini,who were investigating cosmic ray products at theUniversity of BristolinEngland,based on photographic films placed in the Andes mountains.Some of those mesons had about the same mass as the already-known mu "meson", yet seemed to decay into it, leading physicistRobert Marshakto 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 avirtual particle) is also used as force carrier to model thenuclear forceinatomic nuclei(betweenprotonsandneutrons). This is an approximation, as the actual carrier of the strong force is believed to be thegluon,which is explicitly used to model strong interaction between quarks. Other mesons, such as the virtualrho mesonsare used to model this force as well, but to a lesser extent. Following the discovery of the pion, Yukawa was awarded the 1949Nobel Prize in Physicsfor his predictions.

For a while in the past, the wordmesonwas sometimes used to meananyforce carrier, such as"the Z⁰meson ",which is involved in mediating theweak interaction.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 articles:Spin (physics),angular momentum operator,Total angular momentum,andQuantum numbers

Spin(quantum numberS) is avectorquantity that represents the "intrinsic"angular momentumof a particle. It comes in increments of⁠1/2⁠ħ.

Quarksarefermions—specifically in this case, particles having spin⁠1/2⁠(S=⁠1/2⁠).Because spin projections vary in increments of 1 (that is 1ħ), a single quark has a spin vector of length⁠1/2⁠,and has two spin projections, either(S_z= +⁠1/2⁠orS_z=⁠−+1/2⁠).Two quarks can have their spins aligned, in which case the two spin vectors add to make a vector of lengthS= 1,with three possible spin projections(S_z= +1,S_z= 0,andS_z= −1),and their combination is called avector mesonorspin-1triplet. If two quarks have oppositely aligned spins, the spin vectors add up to make a vector of lengthS= 0,and only one spin projection(S_z= 0 ),called ascalar mesonorspin-0singlet. Because mesons are made of one quark and one antiquark, they are found in triplet and singlet spin states. The latter are calledscalar mesonsorpseudoscalar mesons,depending on their parity (see below).

There is another quantity of quantizedangular momentum,called theorbital angular momentum(quantum numberL), that is the angular momentum due to quarks orbiting each other, and also comes in increments of 1ħ.The total angular momentum (quantum numberJ) of a particle is the combination of the two intrinsic angular momentums (spin) and the orbital angular momentum. It can take any value fromJ= |L−S|up toJ= |L+S|,in increments of 1.

Meson angular momentum quantum numbers forL= 0, 1, 2, 3

S	L	P	J	JP
0	0	−	0	0−
	1	+	1	1+
	2	−	2	2−
	3	+	3	3+
1	0	−	1	1−
	1	+	2, 0	2+,0+
	2	−	3, 1	3−,1−
	3	+	4, 2	4+,2+

Particle physicists are most interested in mesons with no orbital angular momentum (L= 0), therefore the two groups of mesons most studied are theS= 1;L= 0 andS= 0;L= 0, which corresponds toJ= 1 andJ= 0, although they are not the only ones. It is also possible to obtainJ= 1 particles fromS= 0 andL= 1. How to distinguish between theS= 1,L= 0 andS= 0,L= 1 mesons is an active area of research inmeson spectroscopy.

P-parity

Main article:Parity (physics)

P-parity is left-right parity, or spatial parity, and was the first of several "parities" discovered, and so is often called just"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 calledparity(P).Gravity,theelectromagnetic force,and thestrong interactionall behave in the same way regardless of whether or not the universe is reflected in a mirror, and thus are said toconserve parity(P-symmetry). However, theweak interactiondoesdistinguish "left" from "right", a phenomenon calledparity violation(P-violation).

Based on this, one might think that, if thewavefunctionfor each particle (more precisely, thequantum fieldfor 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 havenegativeoroddparity (P= −1, or alternativelyP= −), whereas the other particles are said to havepositiveorevenparity (P= +1, or alternativelyP= +).

For mesons, parity is related to the orbital angular momentum by the relation:

$P=\left(-1\right)^{L+1}$

where theLis a result of the parity of the correspondingspherical harmonicof thewavefunction.The "+1" comes from the fact that, according to theDirac 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 (L= 0) have odd parity (P= −1).

C-parity

Main article:C-parity

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.If

$|q{\bar {q}}\rangle =|{\bar {q}}q\rangle$

then, the meson is "Ceven "(C= +1). On the other hand, if

$|q{\bar {q}}\rangle =-|{\bar {q}}q\rangle$

then the meson is "Codd "(C= −1).

C-parity rarely is studied on its own, but more commonly in combination with P-parity intoCP-parity.CP-parity was originally thought to be conserved, but was later found to be violated on rare occasions inweak interactions.

G-parity

Main article:G-parity

G-parity is a generalization of theC-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.

If

$|q_{1}{\bar {q}}_{2}\rangle =|{\bar {q}}_{1}q_{2}\rangle$

then, the meson is "Geven "(G= +1). On the other hand, if

$|q_{1}{\bar {q}}_{2}\rangle =-|{\bar {q}}_{1}q_{2}\rangle$

then the meson is "Godd "(G= −1).

Isospin and charge

Main article:Isospin

Combinations of oneu,d,orsquark and oneu,d,orsantiquark inJ^P= 0⁻configuration form anonet.

Combinations of oneu,d,orsquark and oneu,d,orsantiquark inJ^P= 1⁻configuration also form a nonet.

Original isospin model

The concept of isospin was first proposed byWerner Heisenbergin 1932 to explain the similarities between protons and neutrons under thestrong interaction.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 dubbedisospinbyEugene Wignerin 1937.

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 ofspin.Isospin projections varied in increments of 1 just like those of spin, and to each projection was associated a "charged state".Because the" pion particle "had three" charged states ", it was said to be of isospinI= 1.Its "charged states"
π⁺
,
π⁰
,and
π⁻
,corresponded to the isospin projectionsI₃= +1,I₃= 0,andI₃= −1respectively. Another example is the "rho particle",also with three charged states. Its" charged states "
ρ⁺
,
ρ⁰
,and
ρ⁻
,corresponded to the isospin projectionsI₃= +1,I₃= 0,andI₃= −1respectively.

Replacement by the quark model

This belief lasted untilMurray Gell-Mannproposed thequark modelin 1964 (containing originally only theu,d,andsquarks).The success of the isospin model is now understood to be an artifact of the similar masses of theuanddquarks. Because theuanddquarks have similar masses, particles made of the same number of them also have similar masses.

The exactuanddquark composition determines the charge, becauseuquarks carry charge⁠++2/3⁠whereasdquarks carry charge⁠−+1/3⁠.For example, the three pions all have different charges

• 
  π⁺
  = (
  u
  
  d
  )
• 
  π⁰
  = aquantum superpositionof(
  u
  
  u
  ) and(
  d
  
  d
  )states
• 
  π⁻
  = (
  d
  
  u
  )

but they all have similar masses (c.140 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 thequark modelwas adopted, physicists noted that the isospin projections were related to the up and down quark content of particles by the relation

$I_{3}={\frac {1}{2}}\left[\left(n_{\text{u}}-n_{\bar {\text{u}}}\right)-\left(n_{\text{d}}-n_{\bar {\text{d}}}\right)\right],$

where then-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 addingI₃= +⁠1/2⁠for each positively charged up-or-down quark-or-antiquark (up quarks and down antiquarks), andI₃= −⁠1/2⁠for each negatively charged up-or-down quark-or-antiquark (up antiquarks and down quarks).

Flavour quantum numbers

Main article:Flavour (particle physics) § Flavour quantum numbers

Thestrangenessquantum numberS(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 calledsymmetric,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 bebroken.

It was noted that charge (Q) was related to the isospin projection (I₃), thebaryon number(B) and flavour quantum numbers (S,C,B′,T) by theGell-Mann–Nishijima formula:

$Q=I_{3}+{\frac {1}{2}}(B+S+C+B^{\prime }+T),$

whereS,C,B′,andTrepresent thestrangeness,charm,bottomnessandtopnessflavour quantum numbers respectively. They are related to the number of strange, charm, bottom, and top quarks and antiquark according to the relations:

${\begin{aligned}S&=-(n_{\text{s}}-n_{\bar {\text{s}}})\\C&=+(n_{\text{c}}-n_{\bar {\text{c}}})\\B^{\prime }&=-(n_{\text{b}}-n_{\bar {\text{b}}})\\T&=+(n_{\text{t}}-n_{\bar {\text{t}}}),\end{aligned}}$

meaning that the Gell-Mann–Nishijima formula is equivalent to the expression of charge in terms of quark content:

$Q={\frac {2}{3}}[(n_{\text{u}}-n_{\bar {\text{u}}})+(n_{\text{c}}-n_{\bar {\text{c}}})+(n_{\text{t}}-n_{\bar {\text{t}}})]-{\frac {1}{3}}[(n_{\text{d}}-n_{\bar {\text{d}}})+(n_{\text{s}}-n_{\bar {\text{s}}})+(n_{\text{b}}-n_{\bar {\text{b}}})].$

Classification

See also:List of mesons

Mesons are classified into groups according to theirisospin(I),total angular momentum(J),parity(P),G-parity(G) orC-parity(C) when applicable, andquark(q) content. The rules for classification are defined by theParticle Data Group,and are rather convoluted.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.

Types of mesons

Type	S	L	P	J	JP
Pseudoscalar meson	0	0	−	0	0−
Pseudovector meson	0, 1	1	+	1	1+
Vector meson	1	0, 2	−	1	1−
Scalar meson	1	1	+	0	0+
Tensor meson	1	1, 3	+	2	2+

Nomenclature

Flavourless mesons

Flavourless mesons are mesons made of pair of quark and antiquarks of the same flavour (all theirflavour quantum numbersare zero:S= 0,C= 0,B′= 0,T= 0).The rules for flavourless mesons are:

Nomenclature of flavourless mesons

q q content	I	JPC
		0−+,2−+,4−+,...	1+−,3+−,5+−,...	1−−,2−−,3−−,...	0++,1++,2++,...
u d $\mathrm {\tfrac {u{\bar {u}}-d{\bar {d}}}{\sqrt {2}}}$ d u	1	π+ π0 π−	b+ b0 b−	ρ+ ρ0 ρ−	a+ a0 a−
Mix of u u , d d , s s	0	η η′	h h′	ω ϕ	f f′
c c	0	η c	hc	ψ	χc
b b	0	η b	hb	ϒ	χb
t t	0	η t	ht	θ	χt

In addition

• When thespectroscopic stateof the meson is known, it is added in parentheses.
• When the spectroscopic state is unknown, mass (inMeV/c²) is added in parentheses.
• When the meson is in itsground 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:

Nomenclature of flavoured mesons

Quark	Antiquark
	up	down	charm	strange	top	bottom
up	—		D0	K+	T0	B+
down		—	D−	K0	T−	B0
charm	D0	D+	—	D+ s	T0 c	B+ c
strange	K−	K0	D− s	—	T− s	B0 s
top	T0	T+	T0 c	T+ s	—	T+ b
bottom	B−	B0	B− c	B0 s	T− b	—

In addition

• IfJ^Pis in the "normal series" (i.e.,J^P= 0⁺,1⁻,2⁺,3⁻,...), a superscript ∗ is added.
• If the meson is not pseudoscalar (J^P= 0⁻) or vector (J^P= 1⁻),Jis added as a subscript.
• When thespectroscopic stateof the meson is known, it is added in parentheses.
• When the spectroscopic state is unknown, mass (inMeV/c²) is added in parentheses.
• When the meson is in itsground state,nothing is added in parentheses.

Exotic mesons

Main article:Exotic meson

There is experimental evidence for particles that arehadrons(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 isexotic mesons.

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 theZ(4430),discovered by theBelle experimentin 2007 and confirmed byLHCbin 2014. It is a candidate for being atetraquark:a particle composed of two quarks and two antiquarks.See the main article above for other particle resonances that are candidates for being exotic mesons.

List

Main article:List of mesons

Pseudoscalar mesons

Particle name	Particle symbol	Antiparticle symbol	Quark content	Rest mass(MeV/c2)	IG	JPC	S	C	B'	Mean lifetime(s)	Commonly decays to (>5% of decays)
Pion	π+	π−	u d	139.57018±0.00035	1−	0−	0	0	0	(2.6033±0.0005)×10−8	μ+ + ν μ
Pion	π0	Self	$\mathrm {\tfrac {u{\bar {u}}-d{\bar {d}}}{\sqrt {2}}} \,$[a]	134.9766±0.0006	1−	0−+	0	0	0	(8.4±0.6)×10−17	γ + γ
Eta meson	η	Self	$\mathrm {\tfrac {u{\bar {u}}+d{\bar {d}}-2s{\bar {s}}}{\sqrt {6}}} \,$[a]	547.853±0.024	0+	0−+	0	0	0	(5.0±0.3)×10−19[b]	γ + γ or π0 + π0 + π0 or π+ + π0 + π−
Eta prime meson	η′ (958)	Self	$\mathrm {\tfrac {u{\bar {u}}+d{\bar {d}}+s{\bar {s}}}{\sqrt {3}}} \,$[a]	957.66±0.24	0+	0−+	0	0	0	(3.2±0.2)×10−21[b]	π+ + π− + η or ( ρ0 + γ ) / ( π+ + π− + γ ) or π0 + π0 + η
Charmed eta meson	η c(1S)	Self	c c	2980.3±1.2	0+	0−+	0	0	0	(2.5±0.3)×10−23[b]	See η cdecay modes
Bottom eta meson	η b(1S)	Self	b b	9300±40	0+	0−+	0	0	0	Unknown	See η bdecay modes
Kaon	K+	K−	u s	493.677±0.016	1⁄2	0−	1	0	0	(1.2380±0.0021)×10−8	μ+ + ν μor π+ + π0 or π0 + e+ + ν eor π+ + π0
Kaon	K0	K0	d s	497.614±0.024	1⁄2	0−	1	0	0	[c]	[c]
K-Short	K0 S	Self	$\mathrm {\tfrac {d{\bar {s}}+s{\bar {d}}}{\sqrt {2}}} \,$[e]	497.614±0.024[d]	1⁄2	0−	(*)	0	0	(8.953±0.005)×10−11	π+ + π− or π0 + π0
K-Long	K0 L	Self	$\mathrm {\tfrac {d{\bar {s}}-s{\bar {d}}}{\sqrt {2}}} \,$[e]	497.614±0.024[d]	1⁄2	0−	(*)	0	0	(5.116±0.020)×10−8	π± + e∓ + ν eor π± + μ∓ + ν μor π0 + π0 + π0 or π+ + π0 + π−
D meson	D+	D−	c d	1869.62±0.20	1⁄2	0−	0	+1	0	(1.040±0.007)×10−12	See D+ decay modes
D meson	D0	D0	c u	1864.84±0.17	1⁄2	0−	0	+1	0	(4.101±0.015)×10−13	See D0 decay modes
strange D meson	D+ s	D− s	c s	1968.49±0.34	0	0−	+1	+1	0	(5.00±0.07)×10−13	See D+ sdecay modes
B meson	B+	B−	u b	5279.15±0.31	1⁄2	0−	0	0	+1	(1.638±0.011)×10−12	See B+ decay modes
B meson	B0	B0	d b	5279.53±33	1⁄2	0−	0	0	+1	(1.530±0.009)×10−12	See B0 decay modes
Strange B meson	B0 s	B0 s	s b	5366.3±0.6	0	0−	−1	0	+1	1.470+0.026 −0.027×10−12	See B0 sdecay modes
Charmed B meson	B+ c	B− c	c b	6276±4	0	0−	0	+1	+1	(4.6±0.7)×10−13	See B+ cdecay modes

^[a]^Makeup inexact due to non-zero quark masses.
^[b]^PDG reports theresonance width(Γ). Here the conversion τ =ħ⁄Γis given instead.
^[c]^Strongeigenstate.No definite lifetime (seekaon notesbelow)
^[d]^The mass of the
K⁰
_Land
K⁰
_Sare given as that of the
K⁰
.However, it is known that a difference between the masses of the
K⁰
_Land
K⁰
_Son the order of2.2×10⁻¹¹MeV/c²exists.
^[e]^Weakeigenstate.Makeup is missing smallCP–violatingterm (seenotes on neutral kaonsbelow).

Vector mesons

Particle name	Particle symbol	Antiparticle symbol	Quark content	Rest mass(MeV/c2)	IG	JPC	S	C	B'	Mean lifetime(s)	Commonly decays to (>5% of decays)
Charged rho meson	ρ+ (770)	ρ− (770)	u d	775.4±0.4	1+	1−	0	0	0	~4.5×10−24[f][g]	π± + π0
Neutral rho meson	ρ0 (770)	Self	$\mathrm {\tfrac {u{\bar {u}}-d{\bar {d}}}{\sqrt {2}}}$	775.49±0.34	1+	1−−	0	0	0	~4.5×10−24[f][g]	π+ + π−
Omega meson	ω (782)	Self	$\mathrm {\tfrac {u{\bar {u}}+d{\bar {d}}}{\sqrt {2}}}$	782.65±0.12	0−	1−−	0	0	0	(7.75±0.07)×10−23[f]	π+ + π0 + π− or π0 + γ
Phi meson	ϕ (1020)	Self	s s	1019.445±0.020	0−	1−−	0	0	0	(1.55±0.01)×10−22[f]	K+ + K− or K0 S+ K0 Lor ( ρ + π ) / ( π+ + π0 + π− )
J/Psi	J/ψ	Self	c c	3096.916±0.011	0−	1−−	0	0	0	(7.1±0.2)×10−21[f]	See J/ψ (1S) decay modes
Upsilon meson	ϒ (1S)	Self	b b	9460.30±0.26	0−	1−−	0	0	0	(1.22±0.03)×10−20[f]	See ϒ (1S) decay modes
Kaon	K∗+	K∗−	u s	891.66±0.026	1⁄2	1−	1	0	0	~7.35×10−20[f][g]	See K∗ (892) decay modes
Kaon	K∗0	K∗0	d s	896.00±0.025	1⁄2	1−	1	0	0	(7.346±0.002)×10−20[f]	See K∗ (892) decay modes
D meson	D∗+ (2010)	D∗− (2010)	c d	2010.27±0.17	1⁄2	1−	0	+1	0	(6.9±1.9)×10−21[f]	D0 + π+ or D+ + π0
D meson	D∗0 (2007)	D∗0 (2007)	c u	2006.97±0.19	1⁄2	1−	0	+1	0	>3.1×10−22[f]	D0 + π0 or D0 + γ
strange D meson	D∗+ s	D∗− s	c s	2112.3±0.5	0	1−	+1	+1	0	>3.4×10−22[f]	D∗+ + γ or D∗+ + π0
B meson	B∗+	B∗−	u b	5325.1±0.5	1⁄2	1−	0	0	+1	Unknown	B+ + γ
B meson	B∗0	B∗0	d b	5325.1±0.5	1⁄2	1−	0	0	+1	Unknown	B0 + γ
Strange B meson	B∗0 s	B∗0 s	s b	5412.8±1.3	0	1−	−1	0	+1	Unknown	B0 s+ γ
Charmed B meson†	B∗+ c	B∗− c	c b	Unknown	0	1−	0	+1	+1	Unknown	Unknown

^[f]^PDG reports theresonance width(Γ). Here the conversion τ =ħ⁄Γis given instead.
^[g]^The exact value depends on the method used. See the given reference for detail.

Notes on neutral kaons

There are two complications withneutralkaons:

• Due toneutral kaon mixing,the
  K⁰
  _Sand
  K⁰
  _Lare noteigenstatesofstrangeness.However, theyareeigenstates of theweak force,which determines how theydecay,so these are the particles with definitelifetime.
• Thelinear combinationsgiven in the table for the
  K⁰
  _Sand
  K⁰
  _Lare not exactly correct, since there is a small correction due toCP violation.SeeCP violation in kaons.

Note that these issues also exist in principle for other neutral,flavoredmesons; however, the weak eigenstates are considered separate particles only for kaons because of their dramatically different lifetimes.

See also

• Mesonic molecule
• Standard Model

External links

• Nave, C.R., ed. (2005)."A table of some mesons and their properties".Department of Physics and Astronomy.Hyperphysics.Atlanta, GA:Georgia State University.
• "Particle Data Group".Lawrence Berkeley Laboratory(main page). Lawrence, CA.— Compiles authoritative information on particle properties
• van Beveren, E.; Rupp, G.; Petropoulos, N.; Kleefeld, F. (2003). "The light scalar mesons within quark models".Hadron Physics: Effective Theories of Low Energy QCD.AIP Conference Proceedings. Vol. 660. pp. 353–366.arXiv:hep-ph/0211411.Bibcode:2003AIPC..660..353V.doi:10.1063/1.1570585.S2CID6295609.
• "Naming scheme for hadrons"(PDF).Particle Data Group.Lawrence, CA:Lawrence Berkeley Laboratory.2004.
• "Mesons made thinkable".thingsmadethinkable.com.— An interactive visualisation allowing physical properties to be compared
• Perricone, Mike (22 March 2006)."What happened to the antimatter? Fermilab's DZero experiment finds clues in quick-change meson"(Press release). Batavia, IL:Fermi National Accelerator Laboratory(Fermilab).
• Perricone, Mike (25 September 2006)."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 trillion times a second"(Press release). Batavia, IL:Fermi National Accelerator Laboratory(Fermilab).