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

TL;DR

This paper investigates the exotic $ ext{eta}_1(1855)$ state observed in experiments, proposing a tetraquark interpretation using QCD sum rules and analyzing potential decay modes to understand its internal structure.

Contribution

It introduces a QCD sum rule analysis of the $ ext{eta}_1(1855)$ as a tetraquark and evaluates possible molecular states, offering new insights into its structure.

Findings

$ ext{eta}_1(1855)$ can be interpreted as a tetraquark in the $[1_c]_{ar{s}s} imes[1_c]_{ar{q}q}$ configuration.

Possible decay modes for tetraquark and hybrid states are identified and analyzed.

Two ground states of $ar{s}sar{s}s$ molecular configurations with $1^{-+}$ quantum number are predicted.

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.