QCD axial anomaly enhances the $\eta {\eta }^{\prime }$ decay of the hybrid candidate ${\eta }_1(1855)$

Abstract

We study the hybrid mesons with the exotic quantum number $I^G{J}^{PC}=0^{+}{1}^{-+}$ and investigate their decays into the $\eta {\eta }^{\prime }$, $a_1(1260)\pi$, $f_1(1285)\eta$, $f_1(1420)\eta$, $K^{\ast }(892)\bar{K}$, $K_1(1270)\bar{K}$, and $K_1(1400)\bar{K}$ channels. We find that the QCD axial anomaly enhances the decay width of the $\eta {\eta }^{\prime }$ channel although this mode is strongly suppressed by the small $P$-wave phase space. Our results support the interpretation of the ${\eta }_1(1855)$ recently observed by BESIII as the $\bar{s}sg$ hybrid meson of $I^G{J}^{PC}=0^{+}{1}^{-+}$. The QCD axial anomaly ensures the $\eta {\eta }^{\prime }$ decay mode to be a characteristic signal of the hybrid nature of the ${\eta }_1(1855)$.

Comments: 8 pages, 2 figures, 1 table, references added, to be published in Chin. Phys. Lett