Mesons

Mesons are strongly interacting particles having integral spin. A partial list of some mesons is given in Table:

Some Selected Mesons

Particle	Antiparticle	Charge	Spin (h/2π)	Strangeness	Rest Energy (MeV)	Mean Life (s)	Typical Decay Products
π+	π-	+1	0	0	140	2.6x10-8	µ+ + vµ
π0	π0	0	0	0	135	8.4x10-17	ϒ+ϒ
K+	K-	+1	0	+1	494	1.2x10-8	µ+ + vµ
K0	K-0	0	0	+1	498	0.9x10-10	π+ + π-
η	Η	0	0	0	547	5.5x10-19	ϒ + ϒ
ρ+	ρ-	+1	1	0	770	4.4x10-24	π+ + π0
η’	η’	0	0	0	958	2.2x10-21	η+ π+ +π-
D+	D-	+1	0	0	1869	1.1x10-12	K- +π- +π+
ψ	Ψ	0	1	0	3097	7.6x10-21	e+ + e-
B+	B-	+1	0	0	5279	1.6x10-12	D- +π+ +π-
ϒ	ϒ	0	1	0	9460	1.3x10-20	e+ + e-

Generally, mesons are produced in reactions by the strong interaction; they decay, usually to other mesons or leptons, through the strong, electromagnetic, or weak interactions.

For example, pions can be produced in reactions of nucleons, such as

P + n → p + p + π^-  or  p + n → p + n + π⁰

and the pions can decay according to

π ^- → µ^- + v^-_µ  ( mean life time 2.6 x 10^-8 s)

π⁰  → ϒ + ϒ  ( mean life time 8.4 x 10^-18 s)

where the first decay occurs due to the weak interaction (indicated by the neutrinos and suggested by the mean life) and the second due to the electromagnetic interaction (indicated by the photons and suggested by the mean life).*

*Although neutrinos always indicate a weak-interaction decay, not all weak-interaction decays produce neutrinos. The same is true for photons in electromagnetic decays. 

Mesons octet diagram