This paper presents a detailed analysis of the three-body final state interactions in the B^+ DDK^+ process, whose phase space is sufficient small. To precisely extract the resonance parameters, for instance the χ₂₀/₂ (3930) in the DD invariant mass distributions, in this process, one has to take into account final state interaction, especially the three-body final state interaction. We employ the dispersive Khuri-Treiman formalism, combined with a parameterization of the DD interaction based on Heavy Quark Spin Symmetry. By performing a simultaneous fit to the experimental data from LHCb, BaBar, and Belle collaborations, the scheme with three-body interaction successfully describes the invariant mass distributions of the three two-body subsystems. We precisely extract the pole structures of χ₂₀ (3930) and ψ (3770) as 3. 913-0. 018i~GeV and 3. 764-0. 002i~GeV in B^+ decay. By performing the pole trajectory analysis on a uniformized complex plane, we find that both of them stem from the input bare state.
Hu et al. (Fri,) studied this question.