LIGHT UNFLAVORED MESONS
($\mathit S$ = $\mathit C$ = $\mathit B$ = 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   JSON  (beta) PDGID:
M267

${{\mathit \eta}_{{1}}{(1855)}}$

$I^G(J^{PC})$ = $0^+(1^{- +})$ 
Meson with exotic (non-${{\mathit q}}{{\overline{\mathit q}}}$) quantum numbers. A state decaying into ${{\mathit \eta}}{{\mathit \eta}^{\,'}}$ with possible quantum numbers ${}^{}1{}^{-+}$ was reported earlier in this mass region BARBERIS 2000A in high energy central ${{\mathit p}}{{\mathit p}}$ production and by ALDE 1991B in ${{\mathit \pi}^{-}}{{\mathit p}}$ interactions, see the ${{\mathit f}_{{2}}{(1910)}}$, and the review on "Spectroscopy of Light Meson Resonances."
${{\mathit \eta}_{{1}}{(1855)}}$ MASS   $1855 {}^{+11}_{-9}$ MeV 
 
${{\mathit \eta}_{{1}}{(1855)}}$ WIDTH   $188 \pm19$ MeV 
 
$\Gamma_{1}$ ${{\mathit \eta}}{{\mathit \eta}^{\,'}}$   seen 528
 
FOOTNOTES