= Eta singlet state
{title2=$\eta_1=(u\overline u+d\overline d+s\overline s)/\sqrt3$}
This flavour combination is the invariant scalar in the <octet and singlet in a fundamental SU3 tensor product>. Its isospin and flavour hypercharge vanish. Although it shares the central weight with the <Eta octet state>, it lies in a different <irreducible representation>. Physical eta mixing and the singlet axial anomaly distinguish the mass eigenstates from the pure flavour directions.
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