Doubly charmed tetraquark: isospin channels and diquark-antidiquark interpolators

We perform a lattice simulation to investigate the doubly charmed tetraquark T^+_cc observed by the LHCb collaboration, slightly below the D^*+D^0 threshold, with flavor content ccu̅d̅ and isospin-0. Two-meson interpolators are implemented to explore the isospin quantum numbers I=0 and I=1. We observe attraction near the DD^* threshold for I=0 and repulsion for I=1. Moreover, we also include diquark-antidiquark interpolators to study their effect on the energy spectrum. There is no significant shift in the ground state energy when adding diquark-antidiquark interpolators to the interpolator basis when the heavy quark mass is close to the physical charm quark mass. However, we observe a non-negligible shift in the second energy level. This effect has to be taken into account to extract the scattering amplitude of the T^+_cc. Finally, with a higher mass (close to the bottom quark), the ground state is shifted down significantly. The simulation is performed on N_f=2+1 CLS ensembles with m_π≃ 280 MeV.