SU(3) Classification of p -Wave ηπ and η'π Systems

An exotic meson, the $\pi_1(1400)$ with $J^{PC}=1^{-+}$, has been seen to decay into a p-wave $\eta\pi$ system. If this decay conserves flavor SU(3), then it can be shown that this exotic meson must be a four-quark state ($q\bar q+q\bar q$) belonging to a flavor ${\bf10}\oplus{\bf\bar{10}}$ representation of SU(3). In contrast, the $\pi_1(1600)$ with a substantial decay mode into $\eta'\pi$ is likely to be a member of a flavor octet.