Eta and eta prime mesons

Eta and eta prime mesons

Composition	η  : $\mathrm {\tfrac {u{\bar {u}}+d{\bar {d}}-2s{\bar {s}}}{\sqrt {6}}}$ η′  : $\mathrm {\tfrac {u{\bar {u}}+d{\bar {d}}+s{\bar {s}}}{\sqrt {3}}}$
Statistics	Bosonic
Family	Mesons
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