Possible structure of the newly found exotic state <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>η</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>1855</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>
Bing-Dong Wan, Sheng‐Qi Zhang, Cong‐Feng Qiao
Abstract
Recently, a hadronic state named ${\ensuremath{\eta}}_{1}(1855)$, about 1.86 GeV, was observed in the BESIII experiment. This finding has a peculiar interest due to its exotic quantum number ${J}^{\mathrm{PC}}={1}^{\ensuremath{-}+}$. In this paper, we examine the tetraquark interpretation for the structure of ${\ensuremath{\eta}}_{1}(1855)$ in the configurations of $[{1}_{c}{]}_{\overline{s}s}\ensuremath{\bigotimes}[{1}_{c}{]}_{\overline{q}q}$ and $[{1}_{c}{]}_{\overline{s}q}\ensuremath{\bigotimes}[{1}_{c}{]}_{\overline{s}q}$, and perform a mass spectrum calculation in the framework of QCD sum rules. The results show that the observed ${\ensuremath{\eta}}_{1}(1855)$ could be embedded into the $[{1}_{c}{]}_{\overline{s}s}\ensuremath{\bigotimes}[{1}_{c}{]}_{\overline{q}q}$ 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 $\overline{s}s\overline{s}s$ molecular state with ${1}^{\ensuremath{-}+}$ quantum number and find that there might exist two such ground states.