Coupled-Channel Analysis of the ${\chi }_{c1}\left(3872\right)$ Line Shape with BESIII Data

We perform a study of the ${\chi }_{c1}\left(3872\right)$ line shape using the data samples of ${e}^{+}{e}^{-}\to \gamma {\chi }_{c1}\left(3872\right)$, ${\chi }_{c1}\left(3872\right)\to {D}^{0}{\overline{D}}^{0}{\pi }^{0}$, and ${\pi }^{+}{\pi }^{-}J/\psi $ collected with the BESIII detector. The effects of the coupled channels and the off-shell ${D}^{*0}$ are included in the parametrization of the line shape. The line shape mass parameter is obtained to be ${M}_{X}=\left(3871.63±0.1{3}_{-0.05}^{+0.06}\right)\text{}\text{}\mathrm{MeV}$. Two poles are found on the first and second Riemann sheets corresponding to the ${D}^{*0}{\overline{D}}^{0}$ branch cut. The pole location on the first sheet is much closer to the ${D}^{*0}{\overline{D}}^{0}$ threshold than the other, and is determined to be $7.04±0.1{5}_{-0.08}^{+0.07}\text{}\text{}\mathrm{MeV}$ above the ${D}^{0}{\overline{D}}^{0}{\pi }^{0}$ threshold with an imaginary part $-0.19±0.0{8}_{-0.19}^{+0.14}\text{}\text{}\mathrm{MeV}$.