LIGHT UNFLAVORED MESONS
($\boldsymbol S$ = $\boldsymbol C$ = $\boldsymbol B$ = 0)
For $\mathit I = 1$ (${{\mathit \pi}}$, ${{\mathit b}}$, ${{\mathit \rho}}$, ${{\mathit a}}$): ${\mathit {\mathit u}}$ ${\mathit {\overline{\mathit d}}}$, ( ${\mathit {\mathit u}}$ ${\mathit {\overline{\mathit u}}}−$ ${\mathit {\mathit d}}$ ${\mathit {\overline{\mathit d}}})/\sqrt {2 }$, ${\mathit {\mathit d}}$ ${\mathit {\overline{\mathit u}}}$;
for $\mathit I = 0$ (${{\mathit \eta}}$, ${{\mathit \eta}^{\,'}}$, ${{\mathit h}}$, ${{\mathit h}^{\,'}}$, ${{\mathit \omega}}$, ${{\mathit \phi}}$, ${{\mathit f}}$, ${{\mathit f}^{\,'}}$): ${\mathit {\mathit c}}_{{\mathrm {1}}}$( ${{\mathit u}}{{\overline{\mathit u}}}$ $+$ ${{\mathit d}}{{\overline{\mathit d}}}$ ) $+$ ${\mathit {\mathit c}}_{{\mathrm {2}}}$( ${{\mathit s}}{{\overline{\mathit s}}}$ )
INSPIRE search

${{\boldsymbol \eta}}$ $I^G(J^{PC})$ = $0^+(0^{- +})$ 

We have omitted some results that have been superseded by later experiments. The omitted results may be found in our 1988 edition Physics Letters $\mathbf {B204}$ (1988).
${{\mathit \eta}}$ MASS   $547.862 \pm0.017$ MeV 
${{\mathit \eta}}$ WIDTH   $1.31 \pm0.05$ keV 
${{\boldsymbol \eta}}$ $\boldsymbol C$-NONCONSERVING DECAY PARAMETERS
${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ LEFT-RIGHT ASYMMETRY PARAMETER   $0.0009 {}^{+0.0011}_{-0.0012}$  
${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ SEXTANT ASYMMETRY PARAMETER   $0.0012 {}^{+0.0010}_{-0.0011}$  
${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ QUADRANT ASYMMETRY PARAMETER   $(-9 \pm9) \times 10^{-4}$  
${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ LEFT-RIGHT ASYMMETRY PARAMETER   $0.009 \pm0.004$  
${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ PARAMETER $\beta $ (${\mathit D}{\mathrm -wave}$)   $-0.02 \pm0.07$  (S = 1.3)
${{\boldsymbol \eta}}$ $\boldsymbol CP$-NONCONSERVING DECAY PARAMETER
${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ DECAY-PLANE ASYMMETRY PARAMETER ${{\mathit A}_{{\phi}}}$   $-0.006 \pm0.031$  
ENERGY DEPENDENCE OF ${{\boldsymbol \eta}}$ $\rightarrow$ 3 ${{\boldsymbol \pi}}$ DALITZ PLOTS
PARAMETERS FOR ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$
$\alpha $ PARAMETER FOR ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$   $-0.0288 \pm0.0012$  (S = 1.1)
PARAMETER $\Lambda $ IN ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit \gamma}}$ DECAY   $0.716 \pm0.011$ ${\mathrm {GeV/}}\mathit c{}^{2}$ 
    constrained fit information