The $ψ$(2S) state as a subthreshold pole in electron positron annihilation into $D\bar D$ final states

Abstract: By performing a fit to the merged BES 2008 and BESIII 2024 $e^{+e^-\to} D\bar D$ cross-section data, we find that the $ψ(2\mathrm S)$ subthreshold pole influences this process markedly. The statistical significance of the $ψ(2\mathrm S)$ as a subthreshold pole is 8$σ$. A fit assuming it and seven resonances excels with the fit quality characterized by $χ<sup>2/\mathrm{DOF}=240.4/284$, which means a $p$-value of 97\%. The interference of resonances with the continuum provided by the subthreshold pole changes their shapes, positions, and widths.