Possible structure of the newly found exotic state ${\eta }_1(1855)$

Abstract

Recently, a hadronic state named ${\eta }_1(1855)$, about 1.86 GeV, was observed in the BESIII experiment. This finding has a peculiar interest due to its exotic quantum number $J^{PC}=1^{-+}$. In this paper, we examine the tetraquark interpretation 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 spectrum calculation in the framework of QCD sum rules. The results show that the observed ${\eta }_1(1855)$ could be embedded into the $[1_c{]}_{\bar{s}s}\otimes [1_c{]}_{\bar{q}q}$ configuration. The possible tetraquark and hybrid decay modes are analyzed, which are critical in decoding its 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 that there might exist two such ground states.

Comments: 16 pages, 5 figures, and 1 table. Accepted by PRD