Eta prime meson
Composition  : ≈ $\backslash mathrm\{\backslash tfrac\{u\backslash bar\{u\}\; +\; d\backslash bar\{d\}\; \; 2s\backslash bar\{s${\sqrt{6 

Mean lifetime  : (5.0±0.3)×10^{} s, : (3.2±0.2)×10^{} s 
: ≈ $\backslash mathrm\{\backslash tfrac\{u\backslash bar\{u\}\; +\; d\backslash bar\{d\}\; +\; s\backslash bar\{s${\sqrt{3}}}}}
 statistics = Bosonic
 group = Mesons
 generation =
 interaction = Strong, Weak
 antiparticle = Self
 theorized =
 discovered =
 symbol = ,
 mass = : 547.853±0.024 MeV/c^{2}
: 957.66±0.24 MeV/c^{2}
 decay_particle = :
+ or
+ + or
+ +
:
+ + or
( + ) / ( + + ) or
+ +
 electric_charge = 0 e
 color_charge =
 spin = Integer
 num_spin_states =
}}
The eta () and eta prime meson () are mesons made of a mixture of up, down and strange quarks and their antiquarks. The charmed eta meson () and bottom eta meson () 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 ), due to its very fast decay.
Quark composition
The particles belong to the "pseudoscalar" nonet of mesons which have spin J = 0 and negative parity,^{[1]}^{[2]} and and have zero total isospin, I, and zero strangeness and hypercharge. Each quark which appears in an particle is accompanied by its antiquark (the particle overall is "flavourless") and all the main quantum numbers are zero.
The basic SU(3) symmetry theory of quarks for the three lightest quarks, which only takes into account the strong force, predicts corresponding particles
 $\backslash eta\_1\; =\; \backslash mathrm\{\backslash tfrac\{u\backslash bar\{u\}\; +\; d\backslash bar\{d\}\; +\; s\backslash bar\{s\}\}\{\backslash sqrt\{3\}\}\}$, and
 $\backslash eta\_8\; =\; \backslash mathrm\{\backslash tfrac\{u\backslash bar\{u\}\; +\; d\backslash bar\{d\}\; \; 2s\backslash bar\{s\}\}\{\backslash sqrt\{6\}\}\}$.
The subscripts refer to the fact that η_{1} belongs to a singlet (which is fully antisymmetrical) and η_{8} is part of an octet. However in this case the weak and electromagnetic forces, which can transform one flavour of quark into another, cause a significant, though small, amount of "mixing" of the eigenstates (with mixing angle θ_{P} = 11.5 degrees),^{[3]} so that the actual quark composition is a linear combination of these formulae. That is:
 $\backslash left(\; \backslash begin\{array\}\{cc\}\; \backslash cos\backslash theta\_\backslash mathrm\{P\}\; \&\; \; \backslash sin\backslash theta\_\backslash mathrm\{P\}\; \backslash \backslash \; \backslash sin\backslash theta\_\backslash mathrm\{P\}\; \&\; \backslash cos\backslash theta\_\backslash mathrm\{P\}\; \backslash end\{array\}\backslash right)\; \backslash left(\; \backslash begin\{array\}\{c\}\; \backslash eta\_8\; \backslash \backslash \; \backslash eta\_1\; \backslash end\{array\}\backslash right)\; =\; \backslash left(\; \backslash begin\{array\}\{c\}\; \backslash eta\; \backslash \backslash \; \backslash eta\text{'}\; \backslash end\{array\}\; \backslash right)$.
The unsubscripted name refers to the real particle which is actually observed and which is close to the η_{8}. The is the observed particle close to η_{1}.^{[2]}
The and particles are closely related to the betterknown neutral pion , where
 $\backslash pi^0\; =\; \backslash mathrm\{\backslash tfrac\{u\backslash bar\{u\}\; \; d\backslash bar\{d\}\}\{\backslash sqrt\{2\}\}\}$.
In fact π^{0}, η_{1} and η_{8} are three mutually orthogonal linear combinations of the quark pairs uu, dd and ss; they are at the centre of the pseudoscalar nonet of mesons^{[1]}^{[2]} with all the main quantum numbers equal to zero.
General
The eta was discovered in pionnucleon collisions at the Bevatron in 1961 by A. Pevsner et al. at a time when the proposal of the eightfold way was leading to predictions and discoveries of new particles from symmetry considerations.^{[4]}
The difference between the mass of the η and that of the η' is larger than the quark model can naturally explain. This "ηη' puzzle" is resolved by instantons.
See also
External links
 Eta Meson at the Particle Data Group
References
