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QCD sum rule study on the $f_0(980)$ structure as a pure $K \bar{K}$ bound state

We perform a QCD sum rule analysis for the scalar $f_0(980)$ meson to investigate whether it can be described as a pure bound state of $K$ and $\bar{K}$ mesons. Based on the QCD sum rule with the operators of up to dimension 10 within the operator product expansion, we found that it is hard to treat the $f_0(980)$ as a simple $K\bar{K}$ bound state, which implies that the $f_0(980)$ scalar meson has more complicated structure being mixed states of various configurations.