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Recently, a hadronic state named $\eta_1(1855)$, about 1.86 GeV, was observedin the BESIII experiment. This finding has a peculiar interest due to itsexotic quantum number $J^{PC}=1^{-+}$. In this paper, we examine the tetraquarkinterpretation for the structure of $\eta_1(1855)$ in the configurations of$[1_c]_{\bar{s}s}\otimes[1_c]_{\bar{q}q}$ and$[1_c]_{\bar{s}q}\otimes[1_c]_{\bar{s}q}$, and perform a mass spectrumcalculation in the framework of QCD sum rules. The results show that theobserved $\eta_1(1855)$ could be embedded into the$[1_c]_{\bar{s}s}\otimes[1_c]_{\bar{q}q}$ configuration. The possibletetraquark and hybrid decay modes are analyzed, which are critical in decodingits inner structure. In the same way, we evaluate as well the$\bar{s}s\bar{s}s$ molecular state with $1^{-+}$ quantum number and find thatthere might exist two such ground states.

Possible structure of the newly found exotic state $\eta_1(1855)$