Coupled-channel approach to Tcc+ including three-body effects

A coupled-channel approach is applied to the charged tetraquark state T-cc(+). recently discovered by the LHCb Collaboration. The parameters of the interaction are fixed by a fit to the observed line shape in the three-body (DD0)-D-0 pi(+) channel. Special attention is paid to the three-body dynamics in the T-cc(+) due to the finite life time of the D*. An approach to the T-cc(+) is argued to be self-consistent only if both manifestations of the three-body dynamics, the pion exchange between the D and D* mesons and the finite D* width, are taken into account simultaneously to ensure that three-body unitarity is preserved. This is especially important to precisely extract the pole position in the complex energy plane whose imaginary part is very sensitive to the details of the coupled-channel scheme employed. The (DD0)-D-0 and (DD+)-D-0 invariant mass distributions, predicted based on this analysis, are in good agreement with the LHCb data. The low-energy expansion of the D* D scattering amplitude is performed and the low-energy constants (the scattering length and effective range) are extracted. The compositeness parameter of the T-cc(+) is found to be close to unity, which implies that the T-cc(+) is a hadronic molecule generated by the interactions in the D*D-+(0) and D*D-0(+) channels. Employing heavy-quark spin symmetry, an isoscalar D* D* molecular partner of the T-cc(+) with J(P) = 1(+) is predicted under the assumption that the DD* -D* D* coupled-channel effects can be neglected.

Automated summary

In this study, a coupled-channel approach is applied to investigate the charged tetraquark state T-cc(+) recently discovered by the LHCb Collaboration. The observed line shape in the three-body (DD0)-D-0 pi(+) channel is fitted to determine the parameters of the interaction. Special attention is paid to the three-body dynamics in the T-cc(+) and it is argued that considering both the pion exchange between the D and D* mesons and the finite D* width is essential for a self-consistent approach. It is found that the T-cc(+) is a hadronic molecule generated by the interactions in the D*D-+(0) and D*D-0(+) channels, with a compositeness parameter close to unity. Additionally, a predicted isoscalar D* D* molecular partner of the T-cc(+) is proposed under certain assumptions.