Eta meson

Eta and eta prime mesons

Composition	η : η′ :
Statistics	Bosonic
Interactions	Strong, Weak
Symbol	η, η′
Antiparticle	Self
Mass	η : 547.853±0.024 MeV/c2 η′ : 957.66±0.24 MeV/c2
Mean lifetime	η: 5.0±0.3×10−19 s, η′: 3.2±0.2×10−21 s
Decays into	η : γ + γ or π0 + π0 + π0 or π+ + π0 + π− η′ : π+ + π− + η or (ρ0 + γ) / (π+ + π− + γ) or π0 + π0 + γ
Electric charge	0 e
Spin	Integer

The eta (η) and eta prime meson (η′) are mesons made of a mixture of up, down and strange quarks and their antiquarks. The charmed eta meson (η
c) and bottom eta meson (η
b) are forms of quarkonium; they have the same spin and parity as the light eta but are made of charm quarks and bottom quarks respectively. The top quark is too heavy to form a similar meson (top eta meson, symbol η
t), due to its very fast decay.

The eta was discovered in pion-nucleon collisions at the Bevatron in 1961.

The difference between the mass of the η and that of the η' is larger than the quark model can naturally explain. This "η-η' puzzle" is resolved by instantons.

See also

• List of mesons

External links

• Eta Meson at the Particle Data Group