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

${{\boldsymbol a}_{{1}}{(1640)}}$ $I^G(J^{PC})$ = $1^-(1^{+ +})$

Possibly seen in the study of the hadronic structure in decay ${{\mathit \tau}}$ $\rightarrow$ 3 ${{\mathit \pi}}{{\mathit \nu}_{{\tau}}}$ (ABREU 1998G and ASNER 2000 ).
 ${{\mathit a}_{{1}}{(1640)}}$ MASS $1655 \pm16$ MeV (S = 1.2)
 ${{\mathit a}_{{1}}{(1640)}}$ WIDTH $254 \pm40$ MeV (S = 1.8)