Interpretation of the ${\eta }_1(1855)$ as a $K{\bar{K}}_1(1400)+$ c.c. molecule

Abstract

An exotic state with $J^{PC}=1^{-+}$, denoted by ${\eta }_1(1855)$, was observed by BESIII collaboration recently in $J/\psi \to \gamma \eta {\eta }^{\prime }$. The fact that its mass is just below the threshold of $K{\bar{K}}_1(1400)$ stimulates us to investigate whether this exotic state can be interpreted as a $K{\bar{K}}_1(1400)+$ c.c { molecule or not}. Using the one boson exchange model, we show that it is possible for $K{\bar{K}}_1(1400)$ with $J^{PC}=1^{-+}$ to bind together by taking the momentum cutoff $\Lambda \gtrsim 2$ GeV and yield the same binding energy as the experimental value when $\Lambda \approx 2.5$ GeV. In this molecular picture, the predicted branch ratio $\mathrm{Br}({\eta }_1(1855)\to \eta {\eta }^{\prime })\approx 15\%$ is consistent with the experimental results, which again supports the molecular explanation of ${\eta }_1(1855)$. Relevant systems, namely $K{\bar{K}}_1(1400)$ with $J^{PC}=1^{--}$ and $K{\bar{K}}_1(1270)$ with $J^{PC}=1^{-\pm }$, are also investigated, some of which can be searched for in the future experiments.

Comments: 7 pages, 5 figures